Ubuntu Installation :: Firefox 5 Takes All Available Memory

a few months ago i did a fresh install of ubuntu 11.04 64-bits. it works perfectly. i'm using firefox 5.0, and in about it says mozilla firefox for ubuntu canonical 1.0.

every now and then, firefox behaves like a runaway train and starts using up all available memory, and using 100% processor time. this has been going on for a week or so. the only remedy is to kill firefox and restart it.

i'm not sure what causes this problem, but i am starting to suspect that it may be caused by flash, java, or some other plug-in or add-on that i have installed.

my add-ons are:
- adblock plus 1.3.9
- adblock plus pop-up addon 0.2.7
- delicious bookmarks 2.3.1
- delicious extension 2.3.1
- flash-aid 2.1.1
- global menu bar integration 1.0.6
- memory restart 1.4
- stumbleupon 3.91
- ubuntu firefox modifications 0.9.1

with the exception of memory restart 1.4 all these add-ons have been installed for a long time, without ever causing any problems. the problems started before installing memory restart.

my java version is icedtea, installed from the repository. i'm frequently using sweet home 3d (a java program) that runs without any problem. it doesn't make a difference whether i have sh3d running or not, the ff problem occurs regardless.

i also have installed ubuntu restricted extras version 43. videos videos don't cause problems. vimeo videos cause problems on occasion when switching to high definition and/or to full screen, but that is a known vimeo problem.

the problems certainly start when i don't use my computer for a longer period of time. i have disabled the screen saver/energy saver, but that doesn't seem to solve the problem. today i had the problem shortly after visiting a website, reason why i'm starting to suspect that the problem could be linked to some plug-in that website uses.