Certain Firefox problems can be solved by performing a Clean reinstall. This means you remove Firefox and any leftover program files and then reinstall Firefox. Please follow these steps one by one:

1. Download the latest Desktop version of Firefox from http://www.mozilla.org and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (click Exit from the Firefox or File menu) and confirm all upcoming messages.
3. Now, uninstall Firefox by following the steps mentioned in the Uninstall Firefox article.

IMPORTANT: On Windows, the uninstaller has the option to remove your personal data and settings. Make sure that you do not check this option; otherwise all of your bookmarks, passwords, extensions, user customizations and other Firefox user profile data will be removed from your computer.

After uninstalling Firefox on Windows, delete the "Mozilla Firefox" program folder, located by default in one of these locations:

• (On 32-bit Windows) C:\Program Files\Mozilla Firefox
• (On 64-bit Windows) C:\Program Files (x86)\Mozilla Firefox

1. Go to the Windows Start menu and click on "Computer".
2. In the Explorer window that opens, double click Local Disk (C:) to open the C:\ drive.
3. Find the "Program Files (x86)" folder or "Program Files" folder.
   • On 32-bit Windows, double-click the Program Files folder to open it.
   • On 64-bit Windows, you will see a "Program Files (x86)" folder AND a "Program Files" folder. Open the Program Files (x86) folder.
4. Look for a Mozilla Firefox folder. If you find one, right-click it and select Delete and confirm that you want to move the folder to the Recycle Bin.

Now, go ahead and reinstall Firefox:

1. Double-click the downloaded installation file and go through the steps of the installation wizard.
2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

Please report back to see if this helped you!

This issue has been happening at intervals over the past several releases of FireFox. When I close down, usually all goes well and effectively 'job done'. At other times I get the 'Firefox has stopped working message which among other things reports APPCRASH and the problem file as xul.dll.

As that file is always reloaded to match the new version of Firefox it seems, superficially at least, that there must be another issue.

The problem is that I cannot reliably replicate the issue. Sometimes it does not appear for 10 -20 close down sequences and then it starts happening more or less every time.

It may, perhaps, be related to a plugin, of which I have around a dozen, but selectively disabling, or starting in 'Safe' mode doesn't help because the issue is so intermittent it is difficult to be sure just what 'action' actually helped..

Any ideas.

Hey alanrf, I hope you see this post. I have this same issue. pretty much word for word. I'd like to see what we have in common with this issue outside of just the error and hangs. Like you said, this happens with different versions of firefox 17.0 - 18.0. I run noscript and adblock plus for extensions, for plugins I run shockwave flash and silverlight plugin(adobe acrobat disabled and windows presentation foundation also disabled). I'm on windows vista 64 bit.

Do you use any of these same things for your firefox?

If you have found the reason of these errors I would love to know, this stuff bugs the **** out of me!

I think I may have isolated the probable reason.

I use the Tab Mix Plus plug-in, among a few others, and I have found, over the last couple of weeks, that by disabling the Tab Mix Plus Session Manager option and using the FireFox Session Restore feature the crashes no longer occur.

I have tried cross checking other add ins, including Flash and Adobe, but there was never any consistent improvement.

I am waiting to see a solid month or so of 'success' with this latest test before I will be wholly convinced, but at the moment it is looking good.

HTH

Hello,

Thanks for reporting back! Add-ons are a possibility with causing issues. I will send this off to my colleague so we can look into it as well.

Thanks!!

Make sure you are running the most recent version of tabmix plus, https://addons.mozilla.org/en-US/firefox/addon/tab-mix-plus/, and if you are and the issue still happens, please contact the developer of tabmixplus