Display All Modified Firefox Preferences
If you are using Firefox as a web browser, you have probably made some modifications to it. This can be something simple like a different homepage or closing behavior. You may make sophisticated customizations on about:config as well, for instance, to change network settings or what Firefox displays when a new tab page is opened in the browser.
Modified parameters in about:config are highlighted in bold but the sheer number of them on the page makes the page difficult to browse.
It is possible to display all user set preferences on the about:config page. To do so simply click on the status column header on the page. This sorts preferences so that user modified preferences are listed at the top.
About:support modified Firefox preferences
Good news though that there is a way to display all major modified preferences in Firefox. This is done on the about:support troubleshooting information page.
Simply enter about:support in the Firefox address bar and hit the enter key. This should open the Troubleshooting Information page in the browser.
If you scroll down a bit there, you'll find the modified preferences listing there.
Here you find a listing of all preferences that have been modified in this version of Firefox. Please note that the modifications are user specific and that different modified preferences will be shown for user accounts (unless they are duplicates).
Each modified preference relates directly to an entry on Firefox's about:config listing of preferences. Entries are not linked, and it is not possible to change their value from the troubleshooting page. Best practice, therefore, is to have both the about:support and about:config pages open in windows next to each other. This way, you could copy the preference's name into the about:config filter to find the preferences there easily.
The modified preferences listing can be used to troubleshoot issues in the browser. The information can be copied and pasted into another document as part of the troubleshooting process, for instance for documentation purposes. (via)
Update: The about:support page lists only some modified preferences now, not necessarily all modified preferences. Use the about:config page directly to display all modified pages. Check out this little hack to display all modified preferences on about:config.Advertisement