I'm guessing you used to use something besides osx before your macbook and you are sticking with firefox/chrome because it's what you are used to. But id like to say then i assume you moved o quite a few other mac programs, why not try safari? it's actually a very nice browser(unless you use specific plugins that are made for those other browsers you use, then switching isn't easy)
but safari uses the fewest resources of firefox/chrome/opera. if you ever open up activity monitor while you are browsing you'll see safari doesnt use as much memory or cpu, while just surfing or streaming video, downloading. it's really very efficient, and since it uses less cpu it keeps your computer a lot cooler. One example is netflix(using silverlight plugin), i watch videos on there all the time, with chrome i've seen it go as high as 75% cpu usage, with safari it hovers at maybe 30-50% flash numebrs also show a change between browsers.
I'd recommend giving safari a test drive, and see if it your comp stays cooler with flash. O yeah heres a sidenote, it may not work well with flash. but when you watch full screen your computer will shift more of the processing to the gpu(integrated or discrete) than the cpu. the gpu is much more efficient(cooler) when processing video than the cpu, so you can try watching things full screen. unfortunately if you want to do many things at once, flash won't stay full screen, but it's an idea 🙂
