What I have noticed is that 'fire'fox is nothing like fire on my computer.
Hasnt been, and still isnt.
I have a powerbook G4 667mhz and a internet connection that is 512k. (slow.)
Safari opens in 5 seconds.
Firefox first launch is 30 sec.
I always clear cache to keep the speed optimal each time I open, and when I do Firefox is 30 sec. each time. Otherwise it loads in about 15 seconds.
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Second issue.
The smart bar or whatever - not to smart compared to Safari.
Not saying it doesnt have its merits...but consider this:
When I type a url in safaris web bar it automatically starts to fill in the address. And when I put in "macr" it already puts macrumors in their for me so I dont have to type the whole thing NOR do I have to push the down arrow to make it select macrumors.
Thats pretty smart...you know the spotlight type filling in the blank.
I suppose if they could work out the speed issue, as well as that smart bar issue and then let Flock integrate it into their set up (as Flock is based off of FireFox) I would switch over. (Easier for blogging, etc.)
Until then...its Safari - to bad Apple doesnt put whatever it is that people like from Fox and Flock into the browser.

(or allow as options.)
Peace
dAlen