use '''about:config''' in the location bar to bring up the Add-ons Manager ("Ctrl+Shift+A") then click on the "Get Add-ons" on the left. There are thousands of Add-ons to choose from and I wouldn't put much value on anything suggested there, at least click on the "Learn more" and expand everything and check the extension size. The list is mainly a changing list so you see different add-ons. Whether you agree with me or not, that is what was provided to help you find extensions. BTW, you might want to check your own list of extensions against [http://kb.mozillazine.org/Problematic_extensions Problematic extensions] for extensions to either avoid or watch out for potential problems. Firebug is one such extension, unless you are a developer it would probably be far more trouble to you than it is worth. Now I see you have a different question in your "Show more information" and that you do have a problem with Firebug. The information about an extension being compatible before you download it is available not next to the add button but "helpful" add-on page designers have hidden the most important information at the very bottom where you have to expand "Developer information" and (what you are looking for) "'''Version Information'''". Is It Compatible? :: Add-ons for Firefox :"Are your addons compatible with the next version of Firefox? Find out straight from the Add-ons window!" :https://addons.mozilla.org/firefox/addon/is-it-compatible/ Your question is hard to read because of attempt to indent at beginning of paragraph that triggers fixed font for code, and the fact that the "More information" can not be seen in the question itself. There is a "Preview Reply" that lets you view what it would look like. <br><small>Please mark "Solved" one answer that will best help others with a similar problem -- hope this was it.</small>