EDIT: Please see Clarification: TSF, Firefox and Dragon.
I’m testing Firefox 4. Select-and-say will still not work properly in text fields. (PLEASE NOTE: I encourage you to download the beta and click the Feedback button, then mention lack of select-and-say support under “Firefox made me sad because.” We need numbers.) Also, if you’re able to press keys or you prefer saying “press F6” instead of “go to address,” F6 won’t perform that action until you go to View — Toolbars and uncheck Tabs on Top. If you do want to keep your tabs above the navigation and bookmark toolbars, you’ll have to press Control L to get into the address bar. (By keyboard, I mean. Dragon’s address bar command works regardless.)
Otherwise, it seems to be the same as always. The buttons, tabs and menus are still accessible vocally, and the buttons are more compact, which I like. Do note that add-ons I’ve mentioned here are not yet compatible. I will update when they are.