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That doesn't sound right. My 2520M stays at about 8%, using Firefox. That's still relatively high, but in reality there would only be a few on the screen at once.

I can confirm that an i5-4200U (decent < 1000$ notebook) goes from 2-4% lowest proc frequency to 14% max proc frequency (and the fan starts). Using Firefox. It is clearly noticeable. Of course YMMV

Important thing to note (and most devs forget this):

One does not simply browse only one page at a time anymore

Similar here, current chrome on Windows 7 pulls CPU load from ~8 to 40 % and spins up the fan noticeably.

update: Linux, Chrome

Maybe the animated ones should be left as images so far, otherwise great work with the static icons ++