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How to Change Firefox Proxy Settings Programmatically?

I'm launching Firefox via command line and I'd like to launch a specific Firefox Profile with a proxy. According to this answer on Stackoverflow, Firefox proxy settings are stored in pref.js in the Firefox Profile folder and it is necessary to edit this file to launch FF with a proxy.
I've edited the file as follows:
user_pref("network.proxy.ftp", "1.0.0.1");
user_pref("network.proxy.ftp_port", 00000);
user_pref("network.proxy.gopher", "1.0.0.1");
user_pref("network.proxy.gopher_port", 00000);
user_pref("network.proxy.http", "1.0.0.1");
user_pref("network.proxy.http_port", 22222);
user_pref("network.proxy.no_proxies_on", "localhost, 1.0.0.1");
user_pref("network.proxy.socks", "1.0.0.1");
user_pref("network.proxy.socks_port", 00000);
user_pref("network.proxy.ssl", "1.0.0.1");
user_pref("network.proxy.ssl_port", 00000);
user_pref("network.proxy.type", 1);
Note: the IP address and port used above are for demonstration purposes.
However, I'm encountering two problems:
1) Firefox completely ignores these settings and launches FF without any proxy at all
2) When Firefox exits the text modification is reverted/deleted
Note: When I edited the text file above, Firefox was not running. I know there's a disclaimer at the top of prefs.js:
If you make changes to this file while the application is running, the
changes will be overwritten when the application exits.
But there were no live instances of Firefox running at the time I edited the above file.
Manually creating different FF Profiles (as suggested by another user) with different proxies is not an option as everything needs to be done programmatically, without manual intervention.
Does Firefox still support linking proxy via pref.js? If not, what is the current working solution to launch Firefox via command line with a proxy in Java?
Thanks

A proxy-autoconfig file is what you are looking for.
Docs here.
Define a file name.pac, that contains the javascript function
function FindProxyForURL(url, host)
Inside the file you can use any javscript you'd like to decide what proxy to use. Set the path to your .pac file in the firefox settings, under auto-config proxy. Remember to use a file url.
To setup automatic file switching, simply configure firefox to point towards a single file, and overwrite the file programmatically every time you want it to change. You could keep copies of all options, and simply copy an option file into the target file right before running.
An example of a super simple pac file is this:
function FindProxyForURL (url, host) {
return 'PROXY proxy.example.com:8080; DIRECT';
}
It will always return the identical proxy for all endpoints.
Passwords are not explicitly supported by the pac standard, but there are different ways to approach this. Firefox will prompt you for a login if it thinks it needs one, and you could also embed the password into the url (username:password#proxy.example.com). Additionally, a tool like proxy login automator could allow you to use passwords and to dynamically set the proxy without having to fight with firefox.

JS check if chrome iwallet extension is installed on user chrome browser or not?

I am developing wallet to pay for e-commerce websites.
I need to add a check on the JS page if the user has installed chrome extension ( iwallet ) or not.

As said in a previous answer you can't do that. That's because if such a thing was actually present it will be a privacy issue for the chrome users.
Actually the chrome web store is the only website that has access to such a chrome api.
BUT - looking at the source code of the extension you can check what the extension is altering in you browser or even which messages its listening to.
In the Iwallet source code I found in content-script.js and inpage.js that it sets a special window object property window.IWalletJS and you can simply check if it exist to determine if the extension is installed or not.
As simple as:
if('IWalletJS' in window){
console.log("IWallet is installed", window.IWalletJS);
} else {
console.log("IWallet is not installed");
}
Take a look at the object attached to this property you can check if the user is logged, account name and more.

How to check if a Firefox WebExtension is installed or not with page JavaScript?

I have developed a WebExtension for Firefox and my website works with the extension as a prerequisite. I need to check programmatically whether the extension is installed or not and if not ask the user to install it.
I am not able to find a way how to check this operation of whether my extension is already installed in the user's browser.
Editor note: Methods available in Firefox differ from those available in Chrome, so this question is not a duplicate.

Important note to begin with: A page can't query if an extension is installed without explicit help from the extension. This is done to prevent browser fingerprinting and/or preventing sites from denying content if certain extensions are installed.
WebExtensions are largely built upon the same principles as Chrome extensions. As such, this question is relevant: Check whether user has a Chrome extension installed.
However, some of the best methods available in Chrome are currently unavailable in Firefox:
You can't use external messaging from a webpage (through externally_connectable) as it's not available in FF.
You can't use web-accessible resources for checking presence since Firefox intentionally shields them from fingerprinting:
The files will then be available using a URL like:
moz-extension://<random-UUID>/<path/to/resource>
This UUID is randomly generated for every browser instance and is not your extension's ID. This prevents websites from fingerprinting the extensions a user has installed.
As such, what are your options? The page can't talk directly to the extension context (background), and the background can't directly affect the page; you need a Content script to interact with the page content.
How can page code and a content script communicate? They are isolated from each other unless content script does something about it.
First off, generic tricks that work in both FF and Chrome:
You can create or modify a DOM element on the page from a content script and look for those modifications in the page.
// Content script
let beacon = document.createElement("div");
beacon.classname = browser.runtime.id;
document.body.appendChild(beacon);
// Page script
// Make sure this runs after the extension code
if (document.getElementsByClassName("expected-extension-id").length) {
// Installed
} else {
// Not installed
}
You can use postMessage to communicate between contexts, though it's clunky to use as a bidirectional channel.
Here's documentation and sample WebExtension.
// Content script code
window.postMessage({
direction: "from-content-script",
message: "Message from extension"
}, "*");
// Page code
window.addEventListener("message", function(event) {
if (event.source == window &&
event.data.direction &&
event.data.direction == "from-content-script") {
// Assume extension is now installed
}
});
You can use custom DOM events in a similar way.
There are interesting Firefox-specific approaches as well:
You can share code with the page using exportFunction or cloneInto:
// Content script
function usefulFunction() {
/* ... */
}
const extensionInterface = {
usefulFunction
}
window.wrappedJSObject.extensionInterface =
cloneInto(extensionInterface, window, {cloneFunctions: true});
// Page code
if (typeof window.extensionInterface !== "undefined") {
// Installed
window.extensionInterface.usefulFunction();
} else {
// Not installed
}

HTML transient modal window

We have a legacy web application. At various places it opens a window with the help of Privilege Manager on Firefox to get the needed result.
Some of these windows open a Java applet or a PDF document.
The client machines are updating Firefox and Privilege Manager is gone.
What is the easiest way around it?
The problems are :
There must be only one instance of the pop-up at anyone time. This could be done by selecting appropriate window name on window.open() call.
If the window is opened again (by means of user action), it should not reload but just focus to bring it to the foreground (I have seen I can keep a reference to the window on JavaScript to do that)
It basically really must be transient/modal so that the client cannot leave the current page or reload or any other kind of interaction with the parent window (except opening/refocusing the child window) without closing the child window first. I have no idea how to do that.
Do anyone has an idea how to do that?
The client is only Firefox (it works in a special kiosk configuration) on Linux.
I read somewhere that I could somehow write an extension but I am basically clueless about extensions and its API.
Edit1:
Example of (simplified) legacy code. Not really sure if all the permissions were required, but this is it: This function opens a window that stays over the parent window and prevents any interaction from the user with the parent window.
function fWindowOpen(url, name) {
netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserRead");
netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserWrite");
netscape.security.PrivilegeManager
.enablePrivilege("CapabilityPreferencesAccess");
netscape.security.PrivilegeManager
.enablePrivilege("UniversalPreferencesWrite");
netscape.security.PrivilegeManager
.enablePrivilege("UniversalPreferencesRead");
netscape.security.PrivilegeManager.enablePrivilege("UniversalFileRead");
netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");
window.open(
url,
name,
"screenX=70,dependent=yes,menubar=0,toolbar=0,width=900,height=700,modal=1,dialog=1"
);
}
function fnCapture(){
fWindowOpen("/path/to/document_or_japplet/page","_blank");
}
HTML:
<button value="Capture" property="btnCapture" onclick="javascript:fnCapture();"/>
Edit2: Solution
On a typical extension, on the xul code, define this javascript code:
var dialogExt = {
listener: function(evt) {
// Do work with parameters read through evt.target.getAttribute("attribute_name")
window.openDialog(evt.target.getAttribute("url"), evt.target.getAttribute("name"), evt.target.getAttribute("features"));
}
}
// from examples
document.addEventListener("dialogExtEvent", function(e){ dialogExt.listener(e); }, false, true);
Then, on the web page:
var element = document.createElement("dialogExtElement");
element.setAttribute("url", url);
element.setAttribute("name", name);
element.setAttribute("features", features);
document.documentElement.appendChild(element);
var evt = document.createEvent("Events");
evt.initEvent("dialogExtEvent", true, false);
element.dispatchEvent(evt);
Now, maybe I am missing some security checks to let the code work if it originates from the same host, and how to handle a reference to the document that requested the dialog as means of interaction between the dialog window and it's opener.

The Privilege Manager was deprecated in Firefox 12 and removed in Firefox 17 (briefly restored).
You might want to look into Window.showModalDialog(). However, it is deprecated and is expected to go away within the year, or in 2016 if you go with an extended service release (ESR) of Firefox 38. It may be a temporary solution while you develop an extension.
In order to accomplish the same tasks, you will need to write an extension and ask the user to install it (from Bypassing Security Restrictions and Signing Code, the old information about Privilege Manager):
Sites that require additional permissions should now ask Firefox users to install an extension, which can interact with non-privileged pages if needed.
It is possible to write such an extension using any of the three different extension types:
XUL overlay
Restartless/Bootstrap
Add-on SDK
For the first two types, you would use window.open(). The modal option is in "Features requiring privileges". You will probably also want to look at Window.openDialog().
For the Add-on SDK, you would normally use the open() function in the SDK's window/utils module. Here, again, you will probably want to look at openDialog().
It appears you may be opening content that is supplied from the web in these modal windows. It is unlikely that you will get an extension approved to be hosted on AMO which opens content in such windows which in not included in the add-on release. This does not mean you can not develop the extension and have it installed on your kiosk clients without hosting it on AMO. However, there are additional restrictions in development for Firefox this year which will make this significantly more difficult, see: "Introducing Extension Signing: A Safer Add-on Experience".

You should be able to get similiar window.open behavior, including support for the modal option from the sdk's window/utils module.
You will have to install the onclick listener with a content script, send a message to the addon-main through its port and then open that window from the addon main.

Inject content script into iFrame across domains (but with optional permissions)? [duplicate]

Content Script can be injected programatically or permanently by declaring in Extension manifest file. Programatic injection require host permission, which is generally grant by browser or page action.
In my use case, I want to inject gmail, outlook.com and yahoo mail web site without user action. I can do by declaring all of them manifest, but by doing so require all data access to those account. Some use may want to grant only outlook.com, but not gmail. Programatic injection does not work because I need to know when to inject. Using tabs permission is also require another permission.
Is there any good way to optionally inject web site?

You cannot run code on a site without the appropriate permissions. Fortunately, you can add the host permissions to optional_permissions in the manifest file to declare them optional and still allow the extension to use them.
In response to a user gesture, you can use chrome.permission.request to request additional permissions. This API can only be used in extension pages (background page, popup page, options page, ...). As of Chrome 36.0.1957.0, the required user gesture also carries over from content scripts, so if you want to, you could add a click event listener from a content script and use chrome.runtime.sendMessage to send the request to the background page, which in turn calls chrome.permissions.request.
Optional code execution in tabs
After obtaining the host permissions (optional or mandatory), you have to somehow inject the content script (or CSS style) in the matching pages. There are a few options, in order of my preference:
Use the chrome.declarativeContent.RequestContentScript action to insert a content script in the page. Read the documentation if you want to learn how to use this API.
Use the webNavigation API (e.g. chrome.webNavigation.onCommitted) to detect when the user has navigated to the page, then use chrome.tabs.executeScript to insert the content script in the tab (or chrome.tabs.insertCSS to insert styles).
Use the tabs API (chrome.tabs.onUpdated) to detect that a page might have changed, and insert a content script in the page using chrome.tabs.executeScript.
I strongly recommend option 1, because it was specifically designed for this use case. Note: This API was added in Chrome 38, but only worked with optional permissions since Chrome 39. Despite the "WARNING: This action is still experimental and is not supported on stable builds of Chrome." in the documentation, the API is actually supported on stable. Initially the idea was to wait for a review before publishing the API on stable, but that review never came and so now this API has been working fine for almost two years.
The second and third options are similar. The difference between the two is that using the webNavigation API adds an additional permission warning ("Read your browsing history"). For this warning, you get an API that can efficiently filter the navigations, so the number of chrome.tabs.executeScript calls can be minimized.
If you don't want to put this extra permission warning in your permission dialog, then you could blindly try to inject on every tab. If your extension has the permission, then the injection will succeed. Otherwise, it fails. This doesn't sound very efficient, and it is not... ...on the bright side, this method does not require any additional permissions.
By using either of the latter two methods, your content script must be designed in such a way that it can handle multiple insertions (e.g. with a guard). Inserting in frames is also supported (allFrames:true), but only if your extension is allowed to access the tab's URL (or the frame's URL if frameId is set).

I advise against using declarativeContent APIs because they're deprecated and buggy with CSS, as described by the last comment on https://bugs.chromium.org/p/chromium/issues/detail?id=708115.
Use the new content script registration APIs instead. Here's what you need, in two parts:
Programmatic script injection
There's a new contentScripts.register() API which can programmatically register content scripts and they'll be loaded exactly like content_scripts defined in the manifest:
browser.contentScripts.register({
matches: ['https://your-dynamic-domain.example.com/*'],
js: [{file: 'content.js'}]
});
This API is only available in Firefox but there's a Chrome polyfill you can use. If you're using Manifest v3, there's the native chrome.scripting.registerContentScript which does the same thing but slightly differently.
Acquiring new permissions
By using chrome.permissions.request you can add new domains on which you can inject content scripts. An example would be:
// In a content script or options page
document.querySelector('button').addEventListener('click', () => {
chrome.permissions.request({
origins: ['https://your-dynamic-domain.example.com/*']
}, granted => {
if (granted) {
/* Use contentScripts.register */
}
});
});
And you'll have to add optional_permissions in your manifest.json to allow new origins to be requested:
{
"optional_permissions": [
"*://*/*"
]
}
In Manifest v3 this property was renamed to optional_host_permissions.
I also wrote some tools to further simplify this for you and for the end user, such as
webext-domain-permission-toggle and webext-dynamic-content-scripts. They will automatically register your scripts in the next browser launches and allow the user the remove the new permissions and scripts.

Since the existing answer is now a few years old, optional injection is now much easier and is described here. It says that to inject a new file conditionally, you can use the following code:
// The lines I have commented are in the documentation, but the uncommented
// lines are the important part
//chrome.runtime.onMessage.addListener((message, callback) => {
// if (message == “runContentScript”){
chrome.tabs.executeScript({
file: 'contentScript.js'
});
// }
//});
You will need the Active Tab Permission to do this.