Fix what? What pages do you have loaded in those tabs? Do those pages have images or other embedded media? Your description is so simplistic that it's impossible to tell if there's even a problem.

Fix what? Dude, the pages open at this moment:

NYT
MSNBC
Gmail
Newegg
TR
Three Google search tabs
Four stock quote tabs on Morningstar
Shacknews
AnandTech Forum

None of these pages should take 319MB of RAM.

One other problem with FF is that it just stops responding when I close certain tabs--though I never know which ones will cause that. Wait ten seconds, and it closes the tab and the program resumes. Does this on XP and Vista, on machines with 2GB of RAM and dual-core CPUs.

I'm about ready to move to IE7 at home; already had to do that at work.

They can fix the flash issue while they are at it.

As much as I like FF nothing is keeping me from using IE7, as long as it has tabbed browsing I am happy.

I have fourteen tabs open right now; using 319MB of RAM.

W
T
F
?

When the hell are they going to fix this?

Also the Add-ons and Nice-looking themes.

Theses are not real culprit
but when you add them up more and more,
it surely consumes memory.

agreed. I told everyone that use Firefox to not leave it open for too long. You gotta close it every so often (hours) to allieve the memory use.

The problem is memory fragmentation - if you allocate lots of small bits of memory, then free some of them if the next thing you need to allocate is big then it may not fit in one of the gaps that has been freed so it gets added on to the end. To add to the problems, the OS typically works on a 4k page of memory, so even if there is a tiny piece of that 4k page in use, the OS still has to pull that whole page in to memory to read it if it has been paged out.

The common fix to this is to use a chunk allocator with various pools of memory sizes to keep common sized pieces of memory together and to fill pages up before moving to the next one.

"Thrashing the allocator". Is that like gleaming the cube?

I had so much disk thrashing while running HL2 and Firefox that it finally pushed me over the edge and install another gig.

I believe the problem is this bug:
https://bugzilla.mozilla.org/show_bug.cgi?id=76831

Someone complains that 'it can take 20 seconds or more for Mozilla to redraw the rest of the page' after leaving the browser minimised, so it was 'fixed' by preventing trimming.

The real problem is that FF never releases any memory. Windows apps are supposed to trim their working sets when they're minimized; Firefox doesn't, and they had to write code in a non-standard way to accomplish that. Even if you use the trim_on_minimize config setting to change that, FF sliently goes about and pulls back in all that memory. That doesn't happen by accident: they deliberately wrote it to behave badly.