Uninstall your current Firefox

• https://support.mozilla.com/en-US/kb/Uninstalling%20Firefox
• DO NOT SELECT TO REMOVE USER DATA AND SETTINGS
• Restart your system

Download latest Firefox version using one of these links:

• http://www.mozilla.com/en-US/firefox/new/
• http://www.mozilla.com/en-US/firefox/central/
• http://www.mozilla.com/en-US/firefox/fx/
• http://www.mozilla.com/en-US/firefox/all.html

Install Firefox using the downloaded & saved Firefox installer file

• https://support.mozilla.com/en-US/kb/Installing%20Firefox%20on%20Windows

Check and tell if its working.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

Create a new profile as a test to check if your current profile is causing the problems.

See Basic Troubleshooting: Make a new profile:

• https://support.mozilla.com/kb/Basic+Troubleshooting#w_8-make-a-new-profile

There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins" in case there are still problems.

If that new profile works then you can transfer some files from the old profile to that new profile, but be careful not to copy corrupted files

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox