Ryan at CyberNetNews.com has posted an article about how to fix the memory leak in firefox. Now, this is by no means a REAL fix for the Firefox memory leak, but it certainly does appear to help it quite a bit. This little fix will move Firefox to your hard drive when you minimize it, and as a result it will take up less than 10MB of memory while minimized.
Okay, now here are the few simple steps:
1. Open Firefox and go to the Address Bar. Type in about:config and then press Enter.
2. Right Click in the page and select New -> Boolean.
3. In the box that pops up enter config.trim_on_minimize. Press Enter.
4. Now select True and then press Enter.
5. Restart Firefox.
If you start experiencing any issues just go back and delete the value you just created. I also recommend setting the browser.sessionhistory.max_total_viewers value to 0 because that will prevent Firefox from caching pages for the back button,which can free up some of the memory that gets stolen.
If you want to increase your browsing speeds take a look at the ‘Firefox Speed Boost‘ tweak I posted last month – It works like a charm 
probs is, with my comp, i have enough RAM [ish] but my hdd is sooooo slow (i dont know why, when there were 5400 rpm and 7200 rpm drive available, Acer only shipped it with a 4200 rpm one, i mean, thats ancient tech!!! so i will stick with using my RAM, although, my comp often uses 90% of it it idle (!!!!) its a better option i think