I think almost regardless of it’s performance improvements the real game-changing potential here is the inevitable swathe of add-ons and extensions that will be, and in some cases such as NoScript already are, available.

I don’t think that any web developer who has used it would want to go back to a world without Firebug and I also think that it’s influence on WebKit‘s developer tools is fairly clear to see.

So I really hope that support for Fennec spreads beyond the Nokia 810 soon, and that it’s as instrumental as Firefox was in re-igniting browser development, especially from a developer-tool perspective.