Hello,

Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that turns off some settings, disables most add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• In Firefox 29.0 and above, click the menu button , click Help and select Restart with Add-ons Disabled.
• In previous Firefox versions, click on the Firefox button at the top left of the Firefox window and click on Help (or click on Help in the Menu bar, if you don't have a Firefox button) then click on Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one. Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.

Safe mode would not work; it would result in the same situation where the browser window would hang indefinitely and I would need to force Firefox to shut down.

However, strangely, Firefox is now working, but it is no longer saving my favorite tabs or page history; instead, it clears up every time I restart Firefox (despite settings to save browsing and search form history enabled). Logins and saved passwords seem to work as they did before.

The only changes I made were uninstalling a few extensions and themes, but I am unsure if that caused Firefox to stop hanging.

I am unsure if Firefox will continue to freeze in the future, however, so I am still interested in narrowing things down in that regard.

Thanks for your reply.

Do you have the free version of Malwarebytes or the payed version?

We have seen reports that the payed version can cause issues when not properly configured.

Boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

You can check for problems with the sessionstore.js and sessionstore.bak files in the Firefox profile folder that store session data.

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Multiple_profile_files_created

Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost and you will have to recreate them (make a note or bookmark them if possible).

This is not a cure but will make it easier if Firefox locks up in Windows. <strike>https://support.mozilla.org/questions /997866</strike> {web link}

Fred please do not promote such as the thread was locked for a good reason.

https://support.mozilla.org/en-US/kb/forum-rules-and-guidelines

I have the free version of Malwarebytes, so that was not the cause.

Strangely, Firefox is now working as normal -- no hanging upon startup, no history wipes upon exit. Not sure if it was anything I did (deleting a few stray extensions) or if it fixed itself, but at least it is working again.

Thanks for all suggestions provided.

Do you remember what you removed?

Blank Your Monitor + Easy Reading was one of the extensions. Cogshanks Alt-O-Magic Identifizer was another. I also removed an Add to Amazon Wish List button, and a few themes (all very popular themes so I doubt it was that).

Don't remember any other extensions; sorry. It was only two or three other extensions.