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Why do I keep getting a console error when using VS Code and Live Server?

I'm in the process of learning Javascript. I installed the Live Server extension on VS Code, as well as typing "live-server" into the terminal, to see Chrome's console update upon save. Whenever I have a live server up, I keep getting this message in red in the console:
VM4057 content_script.js:1 Uncaught SyntaxError: Identifier 'WBSAutoFillFormTypeUndetermined' has already been declared (at VM4057 content_script.js:1:1)
The only thing I have at 1:1 is 'use strict';, but even if I remove that I still get the message. All code works otherwise. Is there something I can change to make it stop? And just to be clear, I use either the extension or type live-server. Never both at the same time.

The error comes from the Apple's chrome plugin "iCloud Passwords". Deactivate or remove it and the error will disappear.

Using ios_webkit_debug_proxy on linux

I am trying to use the description from https://github.com/google/ios-webkit-debug-proxy to debug my website on iPhone (Running iOS 7.1.2).
I compiled ios_webkit_debug_proxy, and is running it with
ios_webkit_debug_proxy -d
I then start google-chrome and point it to localhost:9222/ which shows my iPhone, and the website it is currently visiting. I then copy/paste the link address(chrome-devtools://devtools/bundled/devtools.html?host=localhost:9222&page=1) into a new chrome tab, and then I get a debug window which shows
Elements,Network,Sources,Timeline,Profiles,Resources,Audits,Console.
But none of theese buttons shows any real content. There is no dom. No javascript. No output in the console view. No activity in the network. Its like debugging a empty view.
My ios_webkit_debug_proxy -d console, shows a new message, each time my iPhone
visits a new website. But it shows no other activity. THe messages start with something like
ss.remove_fd(7)
ss.recv fd=13 len=0
ss.remove_fd(13)
ss.recv fd=12 len=221
wi.recv[221]:
And they do just as far as I can see, contain the website url, but not any real content from the website.
The console I started chrome from, shows the message:
"Uncaught TypeError: Cannot read property 'frame' of undefined", source: chrome-devtools:/
I am using Fedora 20.
Does anyone have any clue why this does not work ?
Thanks

It isn't clear to me if you switch the browser to localhost:9222/ after you get a pair of lines like:
Listing devices on :9221
Connected :9222 to Will's iPhone (8a48ac86edd4f299xxxxxxxxxxxxxxx)
if you don't see the second line, then it means that probably you have issues with usbmuxd or libimobiledevice.
I've had some issues myself with the proxy, but then i was able to use it with satisfaction. In my experience, there are few things that make the life easier:
1) Run the usbmuxd as root and possibly with options -fv so that it doesn't detach from the tty and you see what happens. In my Debian installation it is run wit a system user in background;
2) In order to avoid the crash of the proxy when an unhandled exception happens don't use the debugger release of your chrome/chromium but instead use a pretty older one https://chrome-devtools-frontend.appspot.com/static/18.0.1025.99/devtools.html (see https://github.com/google/ios-webkit-debug-proxy/issues/63)

Can't send Tokbox "signals" on Firefox

I can send use Tokbox to send "signals", i.e., text messages, on Chrome v36 but not Firefox v32.
Unfortunately Tokbox's JS library TB.min.js is minified so I can't easily figure out the problem. Here's the errors I'm seeing:
no element found ClientEvent:1
TypeError: c is undefined TB.min.js:331
Line 331 of TB.min.js:
c.updateStream(a,b,d)}.bind(this),destroyStream:function(a){c.destroyStream(a)}.bind(this)};this.signal=function(a,b){c.signal(a,b)};

Just tested OpenTokRTC chat (built 100% with OpenTok) on firefox and chrome, they seem to be working
Here's the sample code of how OpenTokRTC is using signaling for chat: https://github.com/opentok/OpenTokRTC/blob/master/public/js/room.js#L297

google chrome bug?

this message appears all the time in chrome developer tool's console:
Port error: Could not establish connection. Receiving end does not exist. miscellaneous_bindings:232
chromeHidden.Port.dispatchOnDisconnect miscellaneous_bindings:232
Error in event handler for 'undefined': Cannot read property 'instanceId' of undefined TypeError: Cannot read property 'instanceId' of undefined
at [object Object].<anonymous> (chrome-extension://mgijmajocgfcbeboacabfgobmjgjcoja/content_js_min.js:2:372)
at chrome-extension://mgijmajocgfcbeboacabfgobmjgjcoja/content_js_min.js:1:182
at miscellaneous_bindings:276:11
at [object Object].dispatch (event_bindings:203:41)
at Object.<anonymous> (miscellaneous_bindings:235:27) event_bindings:207
chrome.Event.dispatch event_bindings:207
chromeHidden.Port.dispatchOnDisconnect miscellaneous_bindings:235
is this a bug in chrome or there is something wrong in my chrome installation?

It seems to be a problem with the Google Dictionary (by Google)
This script doesn't seem to exist or is not accessible by that port.

Based on some googling, this is a problem with a chrome extension, but it may not be clear which. (For me, it was Feedly).
The quickest way to find out which is causing the problem:
Disable all your chrome extensions. (Chrome menu > tools > extensions)
Refresh a page - hopefully the port error should be gone now
Re-enable your extensions one by one, refreshing the page after each, 'til the error pops up again in the console. You should now have your culprit.
I know this could be a pain if there are a lot of extensions :/ personally, I took it as a chance to prune the unused / unworthy extensions while I was going through them.

enabling Firefox 5.0 javascript dump()

I'm going through firefox extension writing bootcamp and somewhere along the way the video's author is speaking about switching browser.dom.window.dump.enabled in about:config to true. This option is no longer present in firefox 5.0. From what I read during my google searches, in ff 4.0 you had to create this preference yourself, and it seems like in firefox 5.0 it doesn't work anymore - I can't seem to dump information to firefox error console any more (regardless of whether console2 is enabled or not).
Relevant code:
Here's how I'm launching the browser:
/usr/bin/iceweasel -profile /some/path -no-remote -jsconsole
And here's the code that only shows the alert, without writing anything to the error console:
onCommand: function(event) {
toJavaScriptConsole("toJavaScriptConsole: hello world");
dump("Hello world!\n");
alert("Hello world!\n");
}
Any idea what I can do to have working dump() called from the ff extension I'm working on in firefox 5.0?

You confused the error console with plain linux console - if you run firefox from terminal you should see the dumps right there.
in-depth explanation

This preference was never present by default - you always had to create it and set to true. Also, the output doesn't go to Error Console, it is rather visible in the terminal you start Firefox from. If you happen to test on Windows you should specify -console command line flag to open a terminal window for the output, on Linux simply starting Firefox from a terminal window will do.