Sorry to hear about your problem. Please do the following to revert to the previous secure version which is 3.6.16

Go to Download Firefox v3.6.16 and download it to the desktop. If necessary, download the file with IE8 or 9 and choose to save it to your desktop when you see the prompt.

Then go to Add/Remove Programs, scroll down to Mozilla Firefox and remove it, choosing to keep your bookmarks, customizations etc., (don't checkmark the box).

Then reboot and delete the folder called Mozilla Firefox at this location: C:\Program Files\Mozilla Firefox

Finally run the installation file you downloaded to the desktop earlier.

Your bookmarks, customizations etc., are maintained in a different location and will become available to you again once you complete the installation.

See also:

• http://kb.mozillazine.org/Firefox_crashes
• Troubleshoot Firefox crashes (closing or quitting unexpectedly)

If you have submitted Breakpad crash reports then post the IDs of one or more Breakpad crash reports (bp-xxxxxxxx-xxxxxxxxx-xxxx-xxxxxxxxxxxx).
You can find the IDs of the submitted crash reports on the about:crashes page.
You can open the about:crashes page via the location bar, like you open a website.