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How to save fullscreen state in Firefox?

Following Mozilla's API document on Fullscreen, I've placed the following code in my website, it simply takes the whole document (html element) and makes the page go fullscreen once the user clicks anywhere in the page, and once there's another click, page goes back to normal.
var videoElement = document.getElementsByTagName('html')[0];
function toggleFullScreen() {
if (!document.mozFullScreen) {
if (videoElement.mozRequestFullScreen) {
videoElement.mozRequestFullScreen();
}
} else {
if (document.mozCancelFullScreen) {
document.mozCancelFullScreen();
}
}
}
window.addEventListener("click", function(e) {
toggleFullScreen();
}, false);
My question is how can I save this fullscreen state so every time that Firefox loads up, that page is still on fullscreen.
Or any workaround? This is for Firefox for Android.

It's an extreme workaround, but you can make your website a progressive web app and put "display": "fullscreen" in its manifest. Then you can launch your site from the home screen and use it like a fullscreen native app.

Following my experiments and the specs, this isn't doable, from client browser javascript
This api need an user interaction. We can't activate the fullscreen by scripting.
From the fullscreen api specification:
Fullscreen is supported if there is no previously-established user
preference, security risk, or platform limitation.
An algorithm is allowed to request fullscreen if one of the following
is true:
The algorithm is triggered by user activation.
The algorithm is triggered by a user generated orientation change.
https://fullscreen.spec.whatwg.org/#model
About activation events:
An algorithm is triggered by user activation if any of the following
conditions is true:
The task in which the algorithm is running is currently processing an
activation behavior whose click event's isTrusted attribute is true.
The task in which the algorithm is running is currently running the
event listener for an event whose isTrusted attribute is true and
whose type is one of:
change
click
dblclick
mouseup
pointerup
reset
submit
touchend
https://html.spec.whatwg.org/multipage/interaction.html#triggered-by-user-activation
We can't trigger fullscreens from scripts, or if so, the script must be triggered by the user.
Including simulating a click won't works, this is regular behavior, made to protect user experience.
With some reflexion, we can't agree more on this, imagine any ads page can launch full screens, the web would be a hell to browse!
You told in comment: «I am the only user here»
What you can do if using unix: (( probably alternatives exists in other os )).
Using midori (a lightweight webkit browser), this will start a real fullscreen.
midori -e Fullscreen -a myurl.html
There is no ways to start firefox or chromium in a fullscreen state from the command line, to my knowledge.
But what is doable is to trigger a F11 click at system level, focusing on the good window, just after the page launch. ((sendkey in android adb shell?))
xdotool can do that.
Here is a pipe command line that will launch firefox with myurl.html, search for the most recent firefox window id, then trigger the F11 key on this window.. (Press F11 again to exit)
firefox myurl.html && xdotool search --name firefox | tail -1 | xdotool key F11
This should be easy to adapt for other browsers.
As last alternative, have a look at electron or nw.js.

take a look at this add on for Firefox, i have not tried it, as I'm posting this from mobile, it's description does say that it can force start in full screen. I'm just quoting their description .
Saves the last state or force start in full screen forever! Simple and
complete for this purpose.
Edit : And the link to it
https://addons.mozilla.org/en-US/firefox/addon/mfull/

What about using localStorage like this?
function goFullScreen() {
if (videoElement.mozRequestFullScreen) {
localStorage.setItem('fullscreenEnabled', true)
videoElement.mozRequestFullScreen();
}
}
window.onload = function () {
if (localStorage.getItem('fullscreenEnabled') === true) {
goFullScreen();
}
};
function toggleFullScreen() {
if (!document.mozFullScreen) {
goFullScreen();
} else {
if (document.mozCancelFullScreen) {
document.mozCancelFullScreen();
localStorage.setItem('fullscreenEnabled', false)
}
}
}
window.addEventListener("click", function(e) {
toggleFullScreen();
}, false)

Escape Full screen plays video if video is paused

I have an HTML video that plays full screen when the user clicks play. If the user hits escape inside of full screen, everything works properly - the video stops playing and exits full screen. However, if the user pauses the video inside of full screen and then hits escape, the video starts playing again causing the sound from the video to loop over the page that is returned to upon exiting full screen. My js controls are as follows:
exitHandler: function(){
vid = Video.vid;
$(Video.featuredVideo).toggleClass('featured-video-show');
if (document.webkitIsFullScreen || document.mozFullScreen || document.msFullscreenElement !== null){
if (vid.paused){
vid.play();
}
else {
vid.pause();
}
}
}
How can I stop the video/audio from starting back up if a user pauses inside of full screen and then hits 'escape' to exit full screen?

Create a variable to keep track of whether you are currently (at the time of handler's execution) exiting or entering fullscreen, and don't fire the play command if you are indeed exiting it. I don't think there are specific event listeners for this, so you may have to write an interval for this. When I faced this issue, I used the following function:
var canFullscreen = function(){
return (
!document.fullscreenElement &&
!document.mozFullScreenElement &&
!document.webkitFullscreenElement &&
!document.msFullscreenElement );
}
This function checks whether we can currently enter fullscreen. If it returns false, then either there is no fullscreen capability (old/weird browser), or you are already in fullscreen. This is the function I ran in the interval to check exactly when the user exits fullscreen (and at that point handled the exit programmatically). If you are instead tracking the keypress of the Escape button, you may put that function there to determine whether you're entering or exiting fullscreen.

How to tell if browser/tab is active, and turn down volume sound when user leave

How can I check if the page is open in the active tab? I want to mute video on my website, when user leave tab. Currently I'm using:
$(window).on('focus', function() {
$("video").prop('muted', false);
});
but when user click on adressbar video is muted, so this is unexpected. Can I avoid this behavior? The best solution is something like at this webpage: http://volkswagen-sportscars.fr/cars/ when user open other tabs in browser, sounds is smoothly turned down. How it's made?

Newer browsers (IE10 and up) have support for the Page Visibility API
The Page Visibility API lets you know when a webpage is visible or in
focus. With tabbed browsing, there is a reasonable chance that any
given webpage is in the background and thus not visible to the user.
When the user minimizes the webpage or moves to another tab, the API
sends a visibilitychange event regarding the visibility of the page.
You can detect the event and perform some actions or behave
differently. For example, if your web app is playing a video, it would
pause the moment the user looks at another browser, and plays again
when the user returns to the tab. The user does not lose their place
in the video and can continue watching.
Used something like this
var hidden, visibilityChange;
if (typeof document.hidden !== "undefined") {
hidden = "hidden";
visibilityChange = "visibilitychange";
} else if (typeof document.mozHidden !== "undefined") {
hidden = "mozHidden";
visibilityChange = "mozvisibilitychange";
} else if (typeof document.msHidden !== "undefined") {
hidden = "msHidden";
visibilityChange = "msvisibilitychange";
} else if (typeof document.webkitHidden !== "undefined") {
hidden = "webkitHidden";
visibilityChange = "webkitvisibilitychange";
}
document.addEventListener(visibilityChange, handleVisibilityChange, false);
function handleVisibilityChange() {
$("video").prop('muted', document[hidden]);
}
DEMONSTRATION

Get hosting XULDocument for a ContentWindow or HTMLDocument in Firefox extension?

I have an Firefox Extension with a XUL overlay containing some Javascript with some event handlers. Among those is an EventListener for DOMContentLoaded. I have a second overlay I only want to load when visiting a certain website.
Here's some of the code I have so far:
var appcontent = document.getElementById("appcontent"); // browser
if (appcontent) appcontent.addEventListener("DOMContentLoaded", onPageLoad, true);
function onPageLoad(event) {
var doc = iEvent.originalTarget; // doc is document that triggered "onload" event
var win = doc.defaultView;
if (doc.nodeName != 'document') return; // only documents
if (win != win.top) return; //only top window.
if (win.frameElement) return; // skip iframes/frames
if(doc.location.href.search('http://somewebsite.com/') > -1) {
//Find XULDocument somehow
//var xulDoc = ??????;
xulDoc.loadOverlay('chrome://myextension/content/secondoverlay.xul', null);
}
}
How can I retrieve the XULDocument hosting the DOM, given the DOMContentLoaded event data?

Well, the XUL window is just window, aka. the global scope.
So the following two lines should both work and should be the same:
window.document.loadOverlay(...);
document.loadOverlay(...);
However, this most is not really what you want, because the XUL window is still the main browser.xul which hosts all content windows. There is no dedicated XUL window per content window!
Loading the second overlay will overlay the whole browser window, not just the "tab" (or whatever) and will stay once you close the tab (content window) or navigate away.
Now, the question is: What do you really want to achieve?
Display some UI (toolbar button, menu, whatever) only for certain pages? Then usually you'd overlay all your stuff once (on the initial load, i.e. in the "first" overlay) and just hide/show your UI according to your rules. See Tabbed Browser for some code snippets when dealing with tab switching and/or page loads.
Or you really want to apply something to the content window itself. Then you'd usually just modify the DOM of the content window directly.

Prevent safari loading from cache when back button is clicked

Got an issue with safari loading old youtube videos when back button is clicked. I have tried adding onunload="" (mentioned here Preventing cache on back-button in Safari 5) to the body tag but it doesn't work in this case.
Is there any way to prevent safari loading from cache on a certain page?

Your problem is caused by back-forward cache. It is supposed to save complete state of page when user navigates away. When user navigates back with back button page can be loaded from cache very quickly. This is different from normal cache which only caches HTML code.
When page is loaded for bfcache onload event wont be triggered. Instead you can check the persisted property of the onpageshow event. It is set to false on initial page load. When page is loaded from bfcache it is set to true.
Kludgish solution is to force a reload when page is loaded from bfcache.
window.onpageshow = function(event) {
if (event.persisted) {
window.location.reload()
}
};
If you are using jQuery then do:
$(window).bind("pageshow", function(event) {
if (event.originalEvent.persisted) {
window.location.reload()
}
});

All of those answer are a bit of the hack. In modern browsers (safari) only on onpageshow solution work,
window.onpageshow = function (event) {
if (event.persisted) {
window.location.reload();
}
};
but on slow devices sometimes you will see for a split second previous cached view before it will be reloaded. Proper way to deal with this problem is to set properly Cache-Control on the server response to one bellow
'Cache-Control', 'no-cache, max-age=0, must-revalidate, no-store'

Yes the Safari browser does not handle back/foreward button cache the same like Firefox and Chrome does. Specially iframes like vimeo or youtube videos are cached hardly although there is a new iframe.src.
I found three ways to handle this. Choose the best for your case.
Solutions tested on Firefox 53 and Safari 10.1
1. Detect if user is using the back/foreward button, then reload whole page or reload only the cached iframes by replacing the src
if (!!window.performance && window.performance.navigation.type === 2) {
// value 2 means "The page was accessed by navigating into the history"
console.log('Reloading');
//window.location.reload(); // reload whole page
$('iframe').attr('src', function (i, val) { return val; }); // reload only iframes
}
2. reload whole page if page is cached
window.onpageshow = function (event) {
if (event.persisted) {
window.location.reload();
}
};
3. remove the page from history so users can't visit the page again by back/forward buttons
$(function () {
//replace() does not keep the originating page in the session history,
document.location.replace("/Exercises#nocache"); // clear the last entry in the history and redirect to new url
});

You can use an anchor, and watch the value of the document's location href;
Start off with http://acme.co/, append something to the location, like '#b';
So, now your URL is http://acme.co/#b, when a person hits the back button, it goes back to http://acme.co, and the interval check function sees the lack of the hash tag we set, clears the interval, and loads the referring URL with a time-stamp appended to it.
There are some side-effects, but I'll leave you to figure those out ;)
<script>
document.location.hash = "#b";
var referrer = document.referrer;
// setup an interval to watch for the removal of the hash tag
var hashcheck = setInterval(function(){
if(document.location.hash!="#b") {
// clear the interval
clearInterval(hashCheck);
var ticks = new Date().getTime();
// load the referring page with a timestamp at the end to avoid caching
document.location.href.replace(referrer+'?'+ticks);
}
},100);
</script>
This is untested but it should work with minimal tweaking.

The behavior is related to Safari's Back/Forward cache. You can learn about it on the relevant Apple documentation: http://web.archive.org/web/20070612072521/http://developer.apple.com/internet/safari/faq.html#anchor5
Apple's own fix suggestion is to add an empty iframe on your page:
<iframe style="height:0px;width:0px;visibility:hidden" src="about:blank">
this frame prevents back forward cache
</iframe>
(The previous accepted answer seems valid too, just wanted to chip in documentation and another potential fix)

I had the same issue with using 3 different anchor links to the next page. When coming back from the next page and choosing a different anchor the link did not change.
so I had
House 1
View House 2
View House 3
Changed to
House 1
View House 2
View House 3
Also used for safety:
// Javascript
window.onpageshow = function(event) {
if (event.persisted) {
window.location.reload()
}
};
// JQuery
$(window).bind("pageshow", function(event) {
if (event.originalEvent.persisted) {
window.location.reload()
}
});
None of the solutions found online to unload, reload and reload(true) singularily didn't work. Hope this helps someone with the same situation.

First of all insert field in your code:
<input id="reloadValue" type="hidden" name="reloadValue" value="" />
then run jQuery:
jQuery(document).ready(function()
{
var d = new Date();
d = d.getTime();
if (jQuery('#reloadValue').val().length == 0)
{
jQuery('#reloadValue').val(d);
jQuery('body').show();
}
else
{
jQuery('#reloadValue').val('');
location.reload();
}
});

There are many ways to disable the bfcache. The easiest one is to set an 'unload' handler. I think it was a huge mistake to make 'unload' and 'beforeunload' handlers disable the bfcache, but that's what they did (if you want to have one of those handlers and still make the bfcache work, you can remove the beforeunload handler inside the beforeunload handler).
window.addEventListener('unload', function() {})
Read more here:
https://developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/1.5/Using_Firefox_1.5_caching