Firefox has a lot of preferences. For illustration, here's a map of all of them that are accessible from the Preferences (Mac) or Options (Windows) windows:

That's seven tabs, one of which contains four sub-tabs (Advanced), over the course of which the user can click on buttons to bring up a further 23 windows or panels, one of which has a further five tabs. That's leaving out the Add-ons Manager, host to preferences for add-ons, and the monster-filled fathoms-deep sea that is about:config.
It's hard to get rid of preferences. Typically, there aren't any that are entirely without worth, and, on an individual pref-by-pref basis, it's hard to argue that removing functionality is worth the small ease-of-use gain of one less item. Over time, though, you're left with a situation that is the opposite of simple.
This is a problem to chip away at in Firefox; for Fennec, it demands immediate attention. The smaller screen on a mobile device and a button-density dictated by the size of a fingertip make it impractical to show a huge number of preferences — assuming that you'd even want to inherit that problem! Another defining characteristic of mobile is that the ratio of power-users to non- is skewed even further to non-power-users than on the desktop. Mobile users are just less likely to want to "configure" their mobile browsers.
For comparison, here's the full set of "Settings" in mobile Safari:
What preferences do you think are absolutely necessary in a mobile browser?
Well, obviously, I'd want a form manager.
Posted by: Joe at August 27, 2008 08:41 PM*ahem*
That screenshot brought Firefox to its knees. To actually pan over it, I had to, um...open it in Safari. :/
Posted by: John Silvestri at August 28, 2008 12:40 AMA little surprised that safari has debug console in it's preferences. But ok. I think safari got most of it. I would include the addons manager (if fennec has addons support of course :)), setting home page, ability to save form data, and password manager. (yeah, I know, adding 4 more options. Though you can consolidate clear cache/history/cookies to be 'clear private data').
Also, we have about:config, so it's all cool :)
Posted by: Cesar at August 28, 2008 01:53 AMI would remove JavaScript & Pop-ups. Who wants to turn then OFF on mobile ? (and why ?)
No Debug Console too.
The preferences dialog was one of the things I really loved about Firefox when I saw it (back when it was still called Phoenix or Firebird).
Posted by: Patrick Dubroy at August 28, 2008 08:40 AMWe can have a small subset of preferences part of the fennec but remaining preferences can be a different xul application. In that case, advanced users have the flexibility to set their preferences and at the same time, we don't overload the fennec.
Posted by: Niranjan at August 28, 2008 11:07 AMAside from relevant security/privacy settings... I'd say language preferences and default search engine.
Posted by: fantasai at August 28, 2008 08:56 PMHmm. Just curious... how did you make that image? Simply capturing screens and stiching it up by hand?
Posted by: Ville at August 31, 2008 04:58 AMVille -- I'm afraid so - screencaptures of the individual panels, and then pasting them into an ever-growing Omnigraffle document. The silver lining here, vs. an automated tool, is that, by the time you're done, you really know the diagram :)
Posted by: Madhava at September 2, 2008 10:42 AM