Follow these instructions to replace the current Firefox.

Download Firefox For All languages And Systems {web link} Save the file. Then;

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86) Mac: Open the "Applications" folder. Linux: Check your user manual.

Look for, and rename any Mozilla or Firefox folders by adding .old to them.

After rebooting the computer, run a registry scanner. Then run the installer. If all goes well, remove the OLD folders when you are done.

Next, this will clean out your user profile, but keep important files.

Refresh Firefox {web link} is a LAST RESORT ! !

Refresh Firefox - reset add-ons and settings

If you're having problems with Firefox, refreshing it can help. The refresh feature fixes many issues by restoring Firefox to its default state while saving your essential information like bookmarks, passwords, and open tabs.

Thanks for the quick replies, Fred! In your first post, run the registry scanner and do WHAT? Remove all references to firefox (can't do mozilla since I also have Thunderbird installed)? Or just remove broken/dead links? Using something link ccleaner?

Sounds like the result of this process would be a virgin Firefox with NO user data at all - bookmarks/history/plugins/tabs/etc. What if all does NOT "go well", how do I get back to where I am now? Would I have to reinstall every extension,userscript,plugin manually, or could I drag them over selectively from the old folders?

In your second post, the "restore feature" would remove extensions and themes, and "reset" all plugins. Somewhat destructive, but recoverable. Which of these two approaches should I try first? And could I do the other one if the one I try first doesn't work?

The first instruction will totally remove Firefox and install a fresh program. The second will reset the profile to factory default, but keep important files.

Firefox comes in two or more folders on all computers. They are;

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And one folder in the profile of each user on the computer.

If you remove the Firefox folder, the user folders would not be affected.

As to Thunderbird, you can always re-install it if needed.

As for running a registry scanner, this is to clean out bad entries. You don't have to do this if you don't want to.

Just to be 100% clear, you are renaming or deleting the

C:\Program Files (x86)\Mozilla Firefox\

folder ONLY, and NOT any of the folders under

C:\Users\

where your valuable Firefox data is stored.

To address your questions more completely, my suggested approach would entail these steps:

(1) Clean Reinstall of the program files (2) New profile to confirm that it works without your data (3) Selective data migration

And to do that...

Clean Reinstall

We use this name, but it's not about removing your settings, it's about making sure the program files are clean (no inconsistent or alien code files). As described below, this process does not disturb your existing settings. Do NOT uninstall Firefox, that's not needed.

(A) Download a fresh installer for Firefox 44.0 from https://www.mozilla.org/firefox/all/ to a convenient location. (Scroll down to your preferred language.)

(B) Exit out of Firefox (if applicable).

(C) Rename the program folder as follows:

(64-bit Windows folder names)

C:\Program Files (x86)\Mozilla Firefox

to

C:\Program Files (x86)\OldFirefox

(32-bit Windows folder names)

C:\Program Files\Mozilla Firefox

to

C:\Program Files\OldFirefox

(D) Run the installer you downloaded in step (A). It should automatically connect to your existing settings.

Does a cleanly reinstalled Firefox start up normally?? If not, you'll need to proceed to the next step.

Note: Some plugins may exist only in that OldFirefox folder. If something essential is missing, look in these folders:

• \OldFirefox\Plugins
• \OldFirefox\browser\plugins

Create a new Firefox profile

A new profile will have your system-installed plugins (e.g., Flash) and extensions (e.g., security suite toolbars), but no themes, other extensions, or other customizations. It also should have completely fresh settings databases and a fresh cache folder.

Start up in the Profile Manager using Start > search box (or Run):

firefox.exe -P

Don't delete anything here!

Any time you want to switch profiles, exit Firefox and return to this dialog.

Click the Create Profile button, assign a name like TEST2016, and skip the option to relocate the profile folder. After creating the profile, select it and start Firefox in that profile.

Does Firefox start successfully? If yes: you can proceed with the third step. If no: some external software on your system may be interfering with Firefox. Do you run Trusteer Rapport banking security software?

When returning to the Profile Manager, you might be tempted to use the Delete Profile button. But... it's a bit too easy to accidentally delete your "real" profile, so I recommend resisting the temptation. If you do want to clean up later, I suggest making a backup of all your profiles first in case something were to go wrong.

Data Migration

This article describes what is in your old profile folder that you might want to copy to the new folder. However, when it comes to extensions, assuming they do not have dozens of settings or a lot of stored data, it is best to reinstall them from their sources.

Recovering important data from an old profile