[jbmorgado]

People are downvoting you just like devs dismiss your bug reports about the issue, but I can tell it is exactly the same for me: Firefox on MacOS is extremely slow and uses too much CPU.

People can blame mine (and many others) particular system as much as they want but the fact remains: FF on some MacOS systems is a big CPU hog while Safari, Chrome and Opera just work fine.

In Linux (with the same plugins) it works rather well though (except when using some stuff like Google docs).