Firefox is getting better all the time, thanks to a new version being released every six weeks. But, even so, the most exciting developments are always happening in the Nightly channel.
Currently, Firefox 15 resides there and it's just gotten a very cool new feature, albeit one that still needs a lot of work, in-tab (in-content) preferences.
Mozilla has been working on removing as many dialogs as possible getting everything to work inside a tab. Google Chrome does the same of course and it's somewhat ahead of Firefox in this respect.
A major hurdle was overcome with the introduction of the in-tab Addon Manager in Firefox 4. Now, in Firefox 15, the entire preferences dialog can similarly be accessed via a regular tab. The feature is not enabled by default, even in Nightly, as it's still in need of plenty of work, but you can check it out by going to about:config and set browser.preferences.inContent to True.
In-Tab Preferences Now in Firefox 15
Firefox is slowly getting rid of annoying window dialogs