How can I upgrade to Firefox 3.6.6 if I cannot open the browser of my current 3.5.10 version?

Question

I can't open my Firexox browser and as I understand, upgrading to a new ff version will fix this problem and keep my settings and bookmarks as well. But how do I upgrade if I can't open my browser?
Alternately I could create a new profile of my current FF version and transfer my settings, but I have to close my current FF session which I can't do without accessing my browser which in turn won't open.
Either way I'm in a catch-22. Is there a solution for either issue?
== This happened ==
Every time Firefox opened
== User Agent ==
Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; GTB6.5; .NET CLR 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)

Answer 1

First, try to determine the reason that Firefox 3.5.10 is hanging or not starting. Since you did not specify, you will need to read some of the following to determine hanging or starting; hanging usually gives you an error message when you try to start Firefox. See below. If you install Firefox 3.6.6 over the top of 3.5.10 and the cause of the hanging or not starting is one or more extensions or plugins or some other cause, Firefox 3.6.6 may experience the same problem.
<u>'''Kill Application'''</u>
In Task Manager, does firefox.exe show in the <u>'''Processes'''</u> tab?
See: [http://kb.mozillazine.org/Kill_application Kill Application]
'''<u>Causes and solutions for Firefox hanging at exit:</u>'''
[[Firefox hangs]]
[http://kb.mozillazine.org/Firefox_hangs#Hang_at_exit Firefox hangs at exit]
[[Firefox is already running but is not responding]]
<u>'''Safe Mode'''</u>
You may need to use '''[[Safe Mode]]''' (click on "Safe Mode" and read) to localize the problem. Firefox Safe Mode is a diagnostic mode that disables Extensions and some other features of Firefox. If you are using a theme, switch to the DEFAULT theme: Tools > Add-ons > Themes <u>'''before'''</u> starting Safe Mode. When entering Safe Mode, do not check any items on the entry window, just click "Continue in Safe Mode". Test to see if the problem you are experiencing is corrected.
See:
'''[[Troubleshooting extensions and themes]]'''
'''[[Troubleshooting plugins]]'''
'''[[Basic Troubleshooting]]'''
If the problem does not occur in Safe-mode then disable all of your Extensions and Plug-ins and then try to find which is causing it by enabling <u>'''one at a time'''</u> until the problem reappears. <u>'''You MUST close and restart Firefox after EACH change'''</u> via File > Restart Firefox (on Mac: Firefox > Quit). You can use "Disable all add-ons" on the Safe mode start window.