there is a lot of information which are not giving. First, which version Firefox have you been using? Was the same version working ok before, or is this a new version. Did you install any addon, in the past four or five days? Addons are a major source of problems. v.6.02 is the latest final version, but I prefer 3.6.22.
Secondly, you may have a profile problem. ((% of the time people waste time uninstalling and reinstalling the program
, which is, rarely, at fault. I am using three versions of Firefox, all with their own profile, and have had no problem of the type you describe.
I suggest that you stop wasting time, and try to run Firefox in Safe Mode, which disable addons. I am not sure if you have that option, in All Programs|Mozilla Firefox, but take a look at it.
Thirdly, you mention that you want to restore the session. I am pretty sure that you have the option of starting a new session. Try that.
UserAgent: Mozilla/5.0 (Windows NT 5.1; rv:7.0) Gecko/20100101 Firefox/7.0