browser.sessionstore.resume_from_crash = false (bug means that session restore always happens, without prompting; this setting turns this off)
dom.ipc.plugins.enabled.npswf32.dll = false (stops plugin-container.exe for Flash. There are other settings if you have Silverlight, Quicktime etc plugins. You may have to create these settings yourself in later versions)
browser.chrome.site_icons and browser.chrome.favicons = false (otherwise wastes time loading site icons)
browser.tabs.animate = false (otherwise get distracting animation when opening tab)
browser.urlbar.trimURLS = false (otherwise http:// protocol bit hidden in location)
layout.spellcheckDefault = 0 (otherwise get distracting red lines in text boxes)
browser.tabs.onTop = false (otherwise tabs appear above URL instead of below)
app.update.enabled = false }
extensions.update.enabled = false } otherwise add-ons update without prompting you
plugins.hide_infobar_for_outdated_plugin (otherwise constant prompts to update Flash etc for minor version changes)
greasemonkey.fileIsGreaseable (otherwise Greasemonkey won't run on local pages)
browser.download.manager.scanWhenDone = false (otherwise FF will, bizarrely, use the Internet Explorer security settings, which generally mean that your downloads get deleted as soon as they complete). You should check this setting before any important download (or use Opera), as I've caught FF setting it back to true more than once. Take note Mozilla, if I wanted to use IE, I'd use IE. I'm guessing that, unless you want the same thing to happen with your add-on downloads, you should set services.sync.prefs.sync.browser.download.manager.scanWhenDone to false too.
Missing status bar: unfixed bug. Missing New Tab button: it won't be on the panel of available buttons when you click Customise, it'll be on the tab bar at the far right. Drag it into place from there.
Having to turn off this whole raft of crap every time there's a new version really puts me off upgrading.
Update: most of these settings are preserved across upgrades. However some crucial ones are not:
- browser.sessionstore.resumefromcrash
- browser.download.manager.scanWhenDone
- services.sync.prefs.sync.browser.download.manager.scanWhenDone
