From Elvanör's Technical Wiki
- Web Developer Toolbar: You can configure this add-on to open a page's source in a tab instead of a window, very useful! Plus you can configure it to open the pages in your favorite editor, but it does not accept command-line argument so you must write a wrapper. You can change the keys shortcuts.
- LiveHTTPHeaders: Extremely useful when you need to analyze what's happening between the browser and the server.
- ColorZilla: Includes an excellent color picker for web design. Unfortunately does not work on 64-bit platforms. Update: does not seem to work anymore even on 32-bit, and latest version (beta 2) prevents Firebug from working.
- HTML Validator: Can be used to see quickly if your pages are W3C compliant. Currently renders Firefox 126.96.36.199 completely unusable.
- Total Validator: Another tool to check page compliance, seems to work better.
- CacheToggle: turns the cache on and off, very useful.
- Rubyfox: Nice theme to relook Firefox.
- A really annoying bug seems to be that Firebug / Firefox error console is not able to catch errors present in Prototype Ajax callbacks. Opera has the same problems. When using normal hand-coded Ajax calls, errors are caught but there still seems to be problems. See this bug.
- If Firebug starts behaving strangely (not logging JS errors in the console). reinstalling it after uninstalling it may help.
- UPDATE: a much better way is to look into prefs.js (in the profile directory) and see if the FB keys seem normal. In my case there was a key set to false which was preventing the logging of JS errors in the console.
- If you have a strange "cannot access optimized closure" message in Firebug (with Firefox 3.5), then you are hitting something else in fact (like accessing an undefined variable). Try to run the script in another browser like Opera to find the real cause.