Take a look
here.
As to "themes," there are lots. And some while saying not compatible can forcibly installed. For instance, my theme is FTDeepDark. The dev only makes it for Windows or UNIX/Linux. But I force-installed the UNIX/Linux one and it works just fine.
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Firefox had themes well before Chrome ever got on the scene. Any FF theme is compatible with T4Fx. See above about my comment on themes.
You can find all this stuff at addons.mozilla.org. Major resource there.
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I'll get a breakdown of what my config file reads when I get home later in order to show some more of the optimizations.
A few addons work wonders too. AdBlockEdge, NoScript, RequestPolicy, etc. All of those can control the crap coming at your browser that bogs things down.
I'll get back to you guys. For now, that link I posted is a pretty good start.