Mashable has a nice rundown of some of the best Firefox add-ons. Now seems as good a time as any to revisit the age-old question of which of the features available today with add-ons (not necessarily the whole add-on, but a feature or capability offered,) should be incorporated into the mainline Firefox distribution.
Now, as usual, I'm on the side of less is more and think we're actually just about right where we are today with features. For those of you afraid of bloat, feel free to recommend a feature cut or removal to make room for something new.
I'll start off. My changes are assuming the bulk of the Firefox 3 PRD is implemented.
I would cut the remaining Web developer tools and make them optional at install-time or part of an alternate Firefox version. This would include Page Source, much of Page Info, and the Error Console. I'd pull DOM Inspector completely and make it an extension for XUL developers. I'd also whack the Page Style feature, Themes, the Character Encoding menus for en-US releases, and the current Work Offline feature. I'd pull the Creative Commons search service.
Having freed up some featurespace, I'd drop "Personas" into the spot formerly occupied by Themes. A personas-like feature would make Themes a lot more popular and easier to use. I'd add Text Area Resizer without a second thought. I'd replace DOM Inspector in the optional install-time developer pack with Firebug. DOM Inspector's a solid XUL developer tool, but Firebug is the tool for Web developers -- a much larger and more important audience. I'd add a light-weight version of Ad Block Plus with a default well-owned and maintained filter list subscription. The subscription would an option within the feature. I'd add a simple Video Download feature, though probably not the existing extension. Users should be able to save anything they see on a page, whether it's an image, a video, or a hunk of text. I'd include something like Link Alert or Target Alert so that people would have more information on the link they're about to click.
That's about it. So, what features from add-ons would you like to see adopted in Firefox?