does it make a difference when you update your graphics driver? http://www.nvidia.com/object/winxp-296.10-whql-driver.html

That sounds awfully high test for our system: we don't run any graphics that we can avoid, don't stream anything or play any online games, get our e-mails as text only, etc. I'm not even sure that our system could run that without slowing down to re-entry velocity.

Is this something that can be done without disturbing other programs or slowing down the operating speed of the computer? I'm open to trying it if no simpler solution comes up, but am not very computer savvy and don't want to risk losing our system, since we depend on it for our business.

Thanks for whatever additional information you can provide.

the new versions of firefox make use of your graphics card when rendering the user-interface or content from the websites you visit. this feature is called hardware acceleration and should - when it is working properly - speed things up, since it shifts processing load from your cpu onto the graphics card.

it is recommended that you use the latest driver (that's the interface between hardware and your operating system) for your graphics card, since newer versions contain all sorts of improvments and bugfixes & they also may resolve rendering errors like the one that you've described. the system details you've provided with your question show that the current graphics driver on your system dates back to 2006, therefore i've pointed you to the up-to-date version.

another route that you can go is to try to switch off support for hardware acceleration in firefox & see if the problem goes away - you can do that in tools > options > advanced > general...