Firefox hang up the whole computer when it is started.

Firefox hang up the whole computer when it is started.

Firstly, create a new Firefox profile:

A new profile will have your system-installed plugins and extensions, but no themes, other extensions, or other customization. It also should come with completely fresh settings databases and a fresh cache folder.

Exit Firefox and start up in the Profile Manager using Start > search box (or Run) -- type or paste the following and press Enter:

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 March4, and ignore the option to change the folder location. Then start Firefox in the new profile you created.

Does Firefox run more normally in the new profile?

If so, it sounds like a settings problem. If not, it could be corruption of Firefox's program files. See the "Clean Reinstall" section below.

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.

To keep the new profile and migrate data, check out this article: Recovering important data from an old profile. We can go over that in more detail as needed.

Secondly, Clean Reinstall:

(1) Download a fresh installer for Firefox 36 from https://www.mozilla.org/firefox/all/ to a convenient location. (Scroll down to your preferred language.)

(2) Exit out of Firefox.

(3) Rename the program folder

(32-bit Windows folder names)

C:\Program Files\Mozilla Firefox

 to

C:\Program Files\OldFirefox

(64-bit Windows folder names)

C:\Program Files (x86)\Mozilla Firefox 

to

C:\Program Files (x86)\OldFirefox

(4) Run the installer you downloaded in #1. It should automatically connect to your existing settings.

When starting Firefox, you may need to use the profile manager to switch back to your regular profile.

Does Firefox run any better with the new program files?

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

1.     \OldFirefox\Plugin
2.   \OldFirefox\browser\plugins