It sounds as though Firefox is trying to load up the windows and tabs you had open in your last session before reinstalling and it running into a problem doing that. How important is it to you to get those windows and tabs back?

If they aren't critical, you may be able to bypass that issue as follows:

Open the Windows Start menu and type or paste the following in the search box:

firefox.exe "https://www.mozilla.org/"

This should launch a single window of Firefox pointed to a page on Mozilla's website. Does that work?

If yes, if you want to restore your previous session, don't close this window. Instead, use the History menu to "Restore Previous Session". Of course, that might take you right back to "not responding"...

If Firefox is unable to load the page, could you check for the issues in this article: Fix problems connecting to websites after updating Firefox.

If Firefox still "hangs" with a Not Responding message, then my next suggestion would be to try to start Firefox in its Safe Mode. That's a standard diagnostic tool to deactivate extensions, some advanced features, and some custom settings. More info: Diagnose Firefox issues using Troubleshoot Mode.

If Firefox is closed, you can start Firefox in its Safe Mode by holding down the Shift key when starting Firefox.

A small dialog should appear: click "Start in Safe Mode" (not Reset)

Any improvement?

I was poking around the system and tried to restart the Firefox from the start menu (instead of the desktop short-cut); this produced a pop-up which offered to start Firefox in Safe Mode or to Reset. I tried the Safe Mode - didn't help. I tried to Reset. It removed the shortcut pinned to task bar but didn't do anything to enable me to start the Firefox browser. I also noticed that in the Windows Task Manager Processes tab I could see a frifox.exe process running and using quite a lot of memory so I killed it.

Will try the steps you recommend although I suspect since I executed the Reset, it is pretty pointless.

Firefox's Reset feature moves your old settings folder to your desktop, inside a folder named Old Firefox Data. Please retain that folder for a few weeks in case you need to recover anything from it.

If the Reset doesn't help, there are two major variables remaining here: possible corruption in settings files (your profile folder) that are carried over after a reset, and possible problems in your Firefox program folder.

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 will have completely fresh settings databases and a fresh cache folder.

Exit Firefox and start up in the Profile Manager using Start > Run (hold Windows key an press R):

firefox.exe -P

Don't delete anything here.

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

Go ahead and click the Create Profile button, give it a name like Nov8, and skip the option to change the folder location. Then start Firefox in the new profile you created.

Until you go back to the Profile Manager and start up in your regular profile, your desktop shortcut should fire up the new profile.

Other than not having any of your settings, does it work normally?

Note: When returning to the Profile Manager, you might be tempted to use the Delete Profile button on your new test profile. 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.

You can replace Firefox's program files without disturbing your settings using this Clean Reinstall procedure:

(1) Download a fresh installer for Firefox 33 from https://www.mozilla.org/firefox/all/ to a convenient location. (Scroll down to your preferred language.)

(2) If applicable, exit out of Firefox or make sure it is fully terminated in Task Manager.

(3) Rename the folder (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.

Does it run?

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

• C:\Program Files (x86)\OldFirefox\Plugins
• C:\Program Files (x86)\OldFirefox\browser\plugins

I have created a new profile for the Firefox and was able run the browser, set a home page navigate to other pages. This seem to have forked for me for now. I will save the other suggestions (for "clean reinstall") in case I need to reinstall Firefox again. I do wonder though why this is suddenly happening. Thank you very much for your help.

You might already have found this article about selectively copying data from your old profile to your new one: Recovering important data from an old profile. Please post back with any questions about the process.