512mb even if there is a underlieing problem I would still upgrade that ram to at least a gig. You can get a 1 gig stick for 20 bucks or so and pop in your PC in about 5 mins. Keep you 512 RAM in so you will have 1.5 gigs ram. As far as firefox goes you may have downloaded some "additional" software when you picked up firefox. I would run msconfig and alt control delete / process to see whats running in the back ground. If you anythign that shouldn't be there look it up for comformation then turn it off/remove it.