1. Change the refresh for live bookmarks
Type about:config, create a new integer value browser.bookmarks.livemark_refresh_seconds and enter the number of seconds for the update interval (default:3600).
2. Change the way Firefox handles keywords typed in the address bar. If you don't type a URL, Firefox sends you to the first result for your query.
Type about:config, write keyword.URL in the Filter, and change the value to
If your query has a clear match (like [slashdot], [stanford]), the functionality will remain. If you enter a general query (like [pizza recipes]), you're sent to the results page.
3. Change the source editor.
Type about:config and edit these values.
view_source.editor.external - open the source with an external application (default: false, change to true)
view_source.editor.path - the path to a text editor like Notepad, Notepad2, NoteTab.
4. Hold down Ctrl when you click on "View image" in the contextual menu to open the image in a new tab. The same trick works for bookmarks, history items, home button, links and can also be done by clicking on the middle button.
5. Move bookmark folders by pressing Shift while using drag&drop.
6. Delete an item from the address bar's history by selecting it with the arrow keys and pressing Shift+Delete.
7. If Adobe Reader crashes your browser go to tools->options->downloads->view and edit actions. Select PDF, change action and choose "Save them on my computer". You can do the same with other file types (like MP3, WMA, MPG).
8. Type / to search in the current page and Ctrl+K to search the web (bring focus to the search box).
9. Duplicate a tab by clicking on the address bar and typing Alt+Enter.
10. Improve memory management.
Firefox 2.0 Beta 1 review
Other great tips from Mozilla.