Chrome on Linux is ~1.47 times faster than Firefox on the Jetstream 3 benchmark as recently reported by Phoronix[0]. That's how we want you to spend the money Mozilla, keeping up with your well-funded rival Google, and making it so we don't end up with a browser monoculture. These sorts of distractions just piss me off, and are not part of your core mission.
Firefox has many weaknesses, but I never once thought “man, that thing is slow”. It isn’t, and chasing benchmark numbers is a waste of effort. A better security model or deeper customizability would be far more valuable.
And regarding (memory) performance, chromium has the "memory saver" settings for unloading tabs. I don't understand why mozilla thinks its acceptable to require users unload tabs manually. Who even does that?
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I remember that Firefox is orders of magnitude more performant in css processing, especially for complex documents with many elements. Can't comment on the javascipt interpeter, so I assume firefox is losing points somewhere else outside the screen painting engine.