I've searched Mozilla's site and the web for help on this problem, but without success: although Mozilla Firefox is normally set to open with only two homepages on my computer, in the last month or so it's been opening with 8 pages that happened to represent one web session I had about a month ago; no matter how I adjust the settings in Tools > Options I can't seem to get it to go back to just opening the original two pages. Further, and more gravely, whenever I'm in FF now it freezes up after about 15 minutes--the top portion of the page disintegrates so that I can barely--if at all--read the taskbar (File, Edit, History, Bookmarks, etc.), and I can't click on links or type into bars--nothing seems active. I can't even close the session w/o doing it down in a bottom toolbar by right-clicking and selecting "Close." Then I open a new FF and the problem begins again about 15 minutes later.
I've troubleshot this only by doing a full Malware scan on my computer and getting rid of the one problem that showed up in that scan. I've also made sure I have all the recent Windows Vista updates.