ihave no idea why it started to do that....it did that to me too, and it started to drive me crazy until i decided to mess around with it about a month ago...it must be a glitch, im not sure...i just set mine for 365 days..glad i could help!
Nice thread. I my opinion, firefox use a lot of memory to do it job. See this picture, 32MB for a browse is too much. Firefox has some other disadvantage, could not display correctly some code which was developed long ago... IE, stupid browse, however, it display perfectly what the web site is design, does not eat much memory... What I use is Maxthon (maxthon.com), you can see all advantage of Firefox and IE at this browse. PS: for more info about firfox history, in Firefox browse, type ABOUT:CACHE in address bar, you will see what you need