Maybe I'm the crazy one here, but I can't remember last time firefox speed was an issue.
You want your software to be really snappy, we all agree on that. But past some point, it's physically impossible for a human to tell the difference. I believe a human can't detect if a tab takes 10ms or 1ms to open.
Firefox has been past the point where "fast" matters for a very long time (and that's a great thing!)