Win 7-10 Users/username/AppData/Roaming/Morzilla/Firefox/Profiles

Before you do any fixing simply rar the whole Morzilla folder inside the roaming folder. Rar without deleting the folder after rar. All your saved passwords and favorites are inside the morzilla/firefox/profiles/number.default

So ones your fox is fixed then you can simply copy paste all from your default folder into your new default folder if you reinstall firefox. Just do replace on the folders with same names.

So to backup your files of firefox you only need to rar that morzilla folder inside the roaming folder. You can even take that rar to another pc install firefox on the other pc , go inside the roaming folder , delete the morzilla folder then unrar your copied morzilla folder.rar and unrar it. Then you get a new folder named morzilla that has your account in it.

After copy-paste, simply start firefox on the new computer and there you go morzilla incl all your favortes and saved passwords. I recommend you to try this on another computer ones you did this ones. Then you know it works and you have a way to move your firefox to any new computer.

After you did that, then you can try to fix your firefox without being afrait to lose your files. Hope it helps you as it helped me ;)

Uninstalling Firefox theu7 the Windows Control Panel and re-installing Firefox won't touch your bookmarks.

The error message about XPCOM usually happens because of a failed Firefox update that left you with a mixture of old and updated files in the Firefox program folder. This can happen in case security software was keeping a handle of some of the files in the Firefox program folder preventing Firefox from replacing all the files. You can do a clean reinstall to ensure that all files are replaced.

Do a clean reinstall of the current Firefox release and delete the Firefox program folder before installing a fresh copy of the current Firefox release.

• Download the Firefox installer and save the file to the desktop
  *https://www.mozilla.org/en-US/firefox/all/

If possible uninstall your current Firefox version to cleanup the Windows Registry and settings in security software.

• Do NOT remove "personal data" when you uninstall your current Firefox version, because this will remove all profile folders and you lose personal data like bookmarks and passwords including data in profiles created by other Firefox versions.

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

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

• It is important to delete the Firefox program folder to remove all the files and make sure there are no problems with files that were leftover after uninstalling.
• http://kb.mozillazine.org/Uninstalling_Firefox

Your personal data like bookmarks is stored in the Firefox profile folder, so you won't lose personal data when you uninstall and reinstall or update Firefox, but make sure NOT to remove personal data when you uninstall Firefox as that will remove all Firefox profile folders and you lose your personal data.

If you keep having problems then create a new profile to test if your current profile is causing the problem.

• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Profile_backup

• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall

(edit: got a confirmation via PM that this reply solved the issue, so I mark it as the solution)