Gfx card nVidia A6600GT with slow behaviour

[RealBlackStuff]

In my PC I have a Winfast A6600GT THD gfx card with 128MB RAM.
Latest 169.21 nVidia drivers.
Since a few days it has deteriorated performance, especially noticeable while visiting TPF and other forums with lots of icons and images.
It looks like it is a Firefox 2.0.0.11 problem, because IE7 performs flawless.
The new FF 3 beta is slightly faster, but still has this same problem.
It manifests as follows:
The header with Charlie appears immediately, followed by 4-5 posts, then the rest of the posts on that page are slowly 'pulled up' one at a time from the bottom of the screen, like a hand organ closing.
There is an enormous amount of data transfer for all the little icons on the left, and it takes about 5 seconds to just display the e.g. T2x/T30 forum.
I have played with various sizes cache, but have not noticed any improvement.

Anyone else have this problem or a suggestion how to fix it?