I really do not like default Firefox theme. It look like a 5 years old kid\’s toy. Unfortunately, up until now alternatives were even worse. Most of them feel like lunatics were creating these terrible greeon-on-black-and-some-red nightmares.

Fortunately, there is a solution now. Somebody had common sense enough to “steal” Safari skin. Oh, well - at least it looks much more pleasant :)
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https://addons.mozilla.org/firefox/1322/