NO. You cannot put that ram in your computer you have right now, and nobody should have been recommending that you try it. That old ram is going to be PC100 or 133 SDRAM most likely. RAM isn't going to be "designed for NT", it has absolutely fuck all to do with the operating system. Pentium IVs will have either DDR or RDRAM, most likely, although I recall some cheap early ones using something else.
SDRAM:
RDRAM:
I use FireFox to take advantage of the NoScript and AdBlocker plugins in particular, but it most definitely isn't faster or better than IE, only somewhat safer. I still use IE sometimes if I'm going to be visiting websites that I know won't have any nasty embedded shit, for speed's sake.