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Firebug has stopped showing me javascript source [duplicate]

Why does Firebug say there is No Javascript on this page when there are clearly loads of JavaScript on the page. I even reloaded the page several time to make sure but it still show the same message.
It never used to do that before, but all of a sudden it misbehaves.
Is it because of some configuration issues or because of something else?

As of Firefox version 50, it seems that Firebug will no longer work as Mozilla are migrating to Firefox Devtools. The tab Tools/Web Developer has a 'debugger' option. See this page for a discussion on the migration. Read all the posts dated 19 November for further information.
It seems to me that the option gives less functionality but Firebug per se is never going to be fixed for Firefox 50 and beyond

EDIT 2017 April
This answer is now outdated and I'm not even testing it anymore because I'm no longer using Firebug (a shame, I loved it years ago in a time it was The tool of trade for web developing).
EDIT 2014 November
The original answer is now more than a year outdated due to firebug evolution.
Thanks to #AmadeusDrZaius to keep it on tracks
Answer for outdated firebug versions
For anyone still with this problem after updating Firebug.
Just click Clear Activation List option inside the Firebug menu.
For those who can't find it, note that "Clear Activation List" shows up in the dropdown from the Firebug icon in the toolbar, but not the Tools > Web Developer > Firebug menu.
I guess due to the bug previous hitting your working page it stays listed as "no activate FB for this site please".

I encountered No Javascript on this page after upgrading Firefox to ver 50.0, with Firebug ver 2.0.18. I tried refreshing Firefox, even completely uninstall Firefox and installed again. Nothing works for me.
A couple of hours later, I downgraded Firefox to 49.0.2, and voila, it works right away. I downloaded the old version here.

I tried everything on this list and nothing worked for me except resetting Firefox like so:
https://support.mozilla.org/en-US/kb/reset-firefox-easily-fix-problems

I realize there are already 10 answers to this question, but in my case none of them helped. I'm running Firefox version 39.0 and Firebug version 2.0.11. The only fix is to completely restart Firefox (i.e. not just the tab or instance with the problem).
Perhaps it's due to Firefox's over-usage of memory, or maybe there's a bug in Firebug. I can't speak to that, but what I do know is it didn't work. I killed Firefox, opened the exact same page again with no changes made and now it works. This has happened to me numerous times and a complete restart always fixes it, but that's the only thing that does.

Since Firefox 49.0 and Firebug 2.0.18 the Script panel is broken. This is due to some internal Firefox API changes. And because Firebug is officially discontinued, this unfortunately won't get fixed anymore.
There was also a bug in Firebug 2.0.11 (and below) in combination with Firefox 39.0 causing this problem. This bug is filed as issue 7918.
It happens when the Script panel is enabled and you close Firebug and reopen it.
You can see two related error messages logged to the Browser Console (can be opened via Ctrl+Shift+J or Firebug menu > Developer > Browser Console):
error occurred while processing 'attach: TypeError: docShell is null
Stack: getChildDocShells#resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/server/actors/webbrowser.js:53:7
...
and
onPacket threw an exception: Error: Server did not specify an actor, dropping packet: {"error":"unknownError","message":"error occurred while processing 'attach: TypeError: docShell is null\nStack: getChildDocShells#resource://gre/modules/commonjs/toolkit/loader.js -> resource://gre/modules/devtools/server/actors/webbrowser.js:53:7
...
Solution:
The only solution until this bug is fixed is to restart Firefox completely.

Similar things have happened to me because I forgot to add the closing tag.
DON'T do this:
<script src="some.url" type="text/javascript">
or
<script src="some.url" type="text/javascript"/>
DO this instead:
<script src="some.url" type="text/javascript"></script>

The same problem just happened to me. I thought that it was a problem in my scripts, but I checked google.com and the problem persisted.
My problem was that I had updated my version of FF and kept the old version of FireBug. When I updated FireBug and everything was solved.

From firefox 49, the fire bug will be built in and it is called fire-bug next. So the fire bug add on won't work properly and no issues will be solved. So you can use firefox inspector. See here for details information

If the problem only shows up on a single page, check that your script folder is referenced from current folder (".") or that's reachable from the server root ("/").
<script src="./scripts/pagescripts.js" type="text/javascript"></script>
may not be the same as
<script src="/scripts/pagescripts.js" type="text/javascript"></script>

As mentioned, sometimes there's a Javascript syntax error that invalidates the whole script. But I have also had this, and simply opening up the page in a new tab or window and refreshing firebug (disable, enable) gets the javascript to show up again.

One time this caught me out was when I published one of my sites and I was checking it out. No Javascript was working, there were no errors in the console and firebug showed no scripts.
It turned out that in that instance, I'd forgotten to allow the site in NoScript - so there really were no scripts being loaded.
Not sure if that's the problem you're facing but it's worth being aware of.

I also got this error when attempting to use Ajax to a different server than the one serving up the page. JavaScript only allows Ajax access to the server that served up the page.

This problem is STILL happening (Aug 2015) with Firefox 39.0.3 and Firebug 2.0.11
For people saying the code is wrong or missing end tags etc. all I did to get all the javascript to reappear in tab was to shut down Firefox and restart it. I didn't change anything. Also that "Clear Activation List" option didn't work (no idea what that means)

I upvoted #Tom_Thomson's answer above, but I am wondering if simply removing and then reinstalling the Firebug add-on might not have accomplished the same thing without losing all the other stuff like bookmarks.

FWIW this problem is still happening in August 2016. I'm using Firebug 2.0.17 with Firefox Dev Edition 50.0a2.
As a workaround, I'm able to use the Developer Tools, though they are not as robust as Firebug (when it's working).

Well Firefox native Inspector is good... I know that you will miss some things, but in general we can survive with it. The good news is... less one addon, FF will be faster :)

Having issues with jquery on internet explorer

I am having issues getting some jquery to work on internet explorer...sometimes it seems to work, and sometimes it doesn't seem to work. Having no issues with chrome/firefox though, i don't understand what can be the cause of these issues.
I am not including the jquery source from the file, but rather putting the file inline the file. I have split it up into a few lines like they do in the actual jquery.min.js though, so that shouldn't be causing any issues.
The rest of the HTML is all on one line though, could the length of this line be causing issues? When clicking some of the links on the page and the listners should activate on the click() function it just opens up the windows explorer tool instead of catching it and having e.preventDefault() activating.
I could show you guys the source for the JS, but I know that is working properly, as I said its fine on chrome/firefox, so I feel there is some hidden issue I don't know about for internet explorer. I have listed all of the possible details and causes of this issue....help please? Thanks to any information and I can answer any questions to get this working :)
EDIT:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-type" content="application/octet-stream" /><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /><!-- JQUERY 1.7.2 HERE --></head><body><!-- HTML IS HERE WITH LOTS OF DIVS --><!-- JQUERY CODE HERE --></body></html>

Had the same issues with javascript, that was running perfectly under Chrome and Firefox and seemed to totally not load on IE, and I was amazed to find out that Internet explorer is not executing your javascript if you have console.log in your code, used for debugging (or other purposes), and thanks to stackoverflow I understood about this.
So if everything in IE seems to work fine with Dev. tools open (F12) then after removing console.log from your scripts everything will be ok.

If you have any console.log statements, take them out. If developer tools are enabled (F12), IE will work. Otherwise, it will stop executing code with console.log.
The best way to test this is open the developer tools, and then see if the code works in IE. If it does, then removing the statements should fix the problem.

Internet Explorer Javascript Slideshow

I have a very strange issue going on here. It's only occurring on Internet Explorer (what a surprise).
Basically I'm trying to fix a site that was given to me after some third-rate developers finished it and obviously did not test on IE.
They've setup a javascript slideshow, now on the pages with the slideshow active, the whole enclosing "body_section" div is being pushed all the way to the left. Have a look for yourselves:
http://sapaconstruction.com.au/sapa/
That's the homepage which floats everything to the left. Now on this page:
http://sapaconstruction.com.au/sapa/?page_id=4
Everything looks normal, so it must have something to do with the javascript slideshow. Here's what the javascript they've written looks like (it's embed on the page).
<script type="text/javascript" src="<?php bloginfo('template_url') ?>/js/compressed.js"></script>
<script type="text/javascript">
$('homeslideshow').style.display='none';
$('wrapper').style.display='block';
var homeslideshow=new TINY.slideshow("homeslideshow");
window.onload=function(){
homeslideshow.auto=true;
homeslideshow.speed=5;
homeslideshow.init("homeslideshow","image","imgprev","imgnext","imglink");
}
</script>
Any help with this issue would be amazing, I've wracked my brain for hours trying hacks and margin fixes and things like that.

Well, I can tell you this. This site has way more problems than just that. In looking at the source, there is a div that comes before the html node. I would first of all fix that, as even in firefox, this is causing some strange things to happen. As a matter of fact, I think this "ieonly" div is what is causing the issue, as in IE this div becomes the wrapper in the body. Whoever built this site was not very familiar with cross browser design, and tried to bake in way too many IE hacks.
EDIT:
The problem was IE was in quirks mode due to the lack of a doctype. The following doctype should work:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

IE stopped showing the main slideshow

Here is a site which I am designing http://ogunsteel.com/eurotech-new/
I am designing this site for last 3 weeks and almost I checked it in 5 browsers Firefox, IE, Chrome, Opera and Safari. All things were going well but today IE stopped showing the main slideshow of the homepage which shows in all other browsers.
IE shows some javascript errors which I am not understanding.....
Addition:
A strange things happening here when I tried with IE8.....when I load the page using IE8 sometimes it shows nothing and sometimes it shows that the page is loaded but some error and the error is " 'imagearray[...].3' is null or not an object" in tab-home.js Line: 41, Char:1
and here is the error code line of tab-home.js file....
if(setting.imagearray[i][3]&&setting.imagearray[i][3].length>setting.longestdesc.length)
setting.longestdesc=setting.imagearray[i][3]}
var slideshow=this
jQuery(document).ready(function($){var setting=slideshow.setting
setting.$wrapperdiv=$('#'+setting.wrapperid).css({position:'relative',visibility:'visible',background:'#444',overflow:'hidden',width:setting.dimensions[0],height:setting.dimensions[1]}).empty()

The error I m seeing in IE8 is
Error: jQuery is undefined
and the error is caused by hoverIntent.js
I've see the source code of your site and I see the hoverIntent.js is included before the jQuery library JS, and it could be a potential problem.
Place the jQuery before all the scripts which uses the jQuery object

JavaScript: Is there a way to get Chrome to break on all errors?

I am looking for an equivalent in Chrome to the "break on all errors" functionality of Firebug. In the Scripts tab, Chrome has a "pause on all exceptions", but this is not quite the same as breaking on all errors.
For instance, when loading a page with the following code, I would like Chrome to break on the line foo.bar = 42. Instead, even when enabling the "Pause on all exceptions", I don't get the expected result.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<script type="text/javascript">
function doError() {
foo.bar = 42;
}
window.onload = function() {
try {
doError();
} catch (e) {
console.log("Error", e);
}
}
</script>
</head>
<body>
</body>
</html>
You can try the code pasted above on this page or using this jsFiddle.

I got trouble to get it so I post pictures showing different options:
Chrome 101.0.4951.64 [27 May 2022]
Very similar UI since at least Chrome 38.0.2125.111 [11 December 2014]
In tab Sources :
When button is activated, you can Pause On Caught Exceptions with the checkbox below:
Previous versions
Chrome 32.0.1700.102 [03 feb 2014]
Chrome 27.0.1453.93 Stable

Edit: The original link I answered with is now invalid.The newer URL would be https://developers.google.com/web/tools/chrome-devtools/javascript/add-breakpoints#exceptions as of 2016-11-11.
I realize this question has an answer, but it's no longer accurate. Use the link above ^
(link replaced by edited above) - you can now set it to break on all exceptions or just unhandled ones. (Note that you need to be in the Sources tab to see the button.)
Chrome's also added some other really useful breakpoint capabilities now, such as breaking on DOM changes or network events.
Normally I wouldn't re-answer a question, but I had the same question myself, and I found this now-wrong answer, so I figured I'd put this information in here for people who came along later in searching. :)

This is now supported in Chrome by the "Pause on all exceptions" button.
To enable it:
Go to the "Sources" tab in Chrome Developer Tools
Click the "Pause" button at the bottom of the window to switch to "Pause on all exceptions mode".
Note that this button has multiple states. Keep clicking the button to switch between
"Pause on all exceptions" - the button is colored light blue
"Pause on uncaught exceptions", the button is colored purple.
"Dont pause on exceptions" - the button is colored gray

Just about any error will throw an exceptions. The only errors I can think of that wouldn't work with the "pause on exceptions" option are syntax errors, which happen before any of the code gets executed, so there's no place to pause anyway and none of the code will run.
Apparently, Chrome won't pause on the exception if it's inside a try-catch block though. It only pauses on uncaught exceptions. I don't know of any way to change it.
If you just need to know what line the exception happened on (then you could set a breakpoint if the exception is reproducible), the Error object given to the catch block has a stack property that shows where the exception happened.

Unfortunately, it the Developer Tools in Chrome seem to be unable to "stop on all errors", as Firebug does.