Please! Have some patience zaibatt! We are just a few volunteers here. But even if highly paid to be at your call 24/7/365, a response within 2 minutes is not a rational expectation. And for fewer delays to resolution to problems, it is best to provide complete information about the hardware, to include version of Windows, PC or motherboard brand and model, and graphics solution, as a minimum.
The CPU is not your problem. Firefox has no limit to the number of tabs it can manage, so that is not your problem. Every page and tab consumes memory. 512Mb is barely enough for the operating system, hardware drivers, and necessary security programs that are running at idle just after a boot. Add the other programs you have running at start, and those you open manually, and you have consumed a large chunk of your available memory. Start opening tabs and chunk by chunk, your RAM is gone. Research your motherboard, check your manual and increase your RAM - I recommend a
minimum of 1 Gb for single core CPUs, and 2Gb for multi-core CPUs for XP, and 2Gb for Vista/Win7.
With only 512Mb you are thrashing the slow (compared to RAM speeds) hard drive by constant Page File use. The Page File needs space and the operating system need lots of free disk space for all sorts of temporary background tasks - make sure you have plenty. Defrag if it has been awhile - XPs own defragger is just fine. Buy a new drive if necessary.
And if you are letting XP manage your Page File, it is most likely set to 768 max (512 x 1.5). That is not enough for what you want to do. I would set the initial and maximum to 1024 then watch Task Manager Performance tab to see how much of it you are using, adjusting as necessary.