The following error appears on the Error Console when bringing up the Applications tab: Error: uncaught exception: [Exception... "Component returned failure code: 0x80570016 (NS_ERROR_XPC_GS_RETURNED_FAILURE) [nsIJSCID.getService]" nsresult: "0x80570016 (NS_ERROR_XPC_GS_RETURNED_FAILURE)" location: "JS frame :: chrome://browser/content/preferences/applications.js :: <TOP_LEVEL> :: line 478" data: no] The Applications tab is then completely empty and it's impossible to take any action, probably as a result of the above error. I tried with a clean profile. Same thing. Reproducible: Always
Although I don't have any idea what causes this, Firefox 3.1 Alpha has a working Applications tab. Meanwhile you can edit the contents in: ~/.mozilla/firefox/<profile>/mimeTypes.rdf
*** This bug has been marked as a duplicate of bug 228665 ***