For me the dealkiller with Firefox is the lack of keychain support. I'm a keychain addict... I have hundreds of keychain entries for websites etc, and I'll be damned if I'll type all that crap in again to Firefox's proprietary and uncertainly protected Password vault. Why bother with a proprietary system when apple has such a nice system-wide built-in? Other than that, it seems pretty nice and is very compatible with all the sites I tried it on.
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