This extension will open source code files from http://mxr.mozilla.org in an editor on the users machine. Currently, this Simply right click on the loaded page and select the Open in Editor option from the pop up context menu. The user may choose any editor through preference settings. If no preferences are selected the extension does not work with OS Xdefaults to gedit on Linux, and only supports notepad.exe for on Windows , and gedit for Linux(currently) nothing on OS X.

Download: http://jamesbostonzenit.senecac.on.ca/extensionswiki/imgs/openineditorOpenineditor.xpi