Settings and Configuration
The configuration can be accessed by going to 'about:config' in the address bar. This loads the config page.
To use a proxy, go to Tools>Options>Advanced>Network>Settings and choose 'Manual proxy configuration' (default is 'Direct connection to the internet'). Enter proxy settings and check 'Use this proxy for all server protocols'.
In FireFox 2.0, the 'Close Tab' 'X' button is on each tab. To change this, go to the config page and filter for 'browser.tabs.closeButtons'. The default value of '1' displays the button on each tab. '3' is FireFox 1.x behavior.
To start FireFox in Safe Mode, you can go to Run and type 'firefox -safe-mode'.
A security warning "Domain Name Mismatch" might make logging into secure domains, like web servers, troublesome. See the extension addons.mozilla.org/firefox/2131
To clear browsing history, saved form history and search history, etc., go to Tools>Clear Private Data, and select what you want to clear. Form history is used in "%Application Data%/Mozilla/Firefox/Profiles/[...].default/formhistory.dat". To overwrite this file with a backup copy, you must first exit FireFox and then copy over it (even if you copy over it in DOS while FireFox is running, it won't work - you must quit FireFox first). Firefox browsing history is in history.dat.
If you want to get rid of a cached autocomplete URL, a URL which shows up in the address bar when you type (e.g. because it's a typo), highlight the URL by scrolling down to it and hit SHIFT+Delete.
One issue many encounter is that the downloading a file causes Firefox to hang - there is a 5-10 second download delay, and the program hangs. The solution is to clear the Downloads cache, either with Tools>Downloads (or CTRL+j) and hitting "Clean Up", or manually deleting downloads.rdf in the Firefox profile folder.
To view the source code of frames, right-click inside the frame, and go to This Frame>View Frame Source.
The Google Toolbar might make FireFox slow. To fix this, go to the extensions Options for it, and disable ""Subscribe" to page content.