If you have ever played around with the preferences setting in Firefox (by typing about:config into the address bar), you may find out that you can quickly and easily add them to the list. Deleting them, however seems to be a lot harder. Basic commands such as pressing delete (or any such combination) don’t seem to work, neither is a delete menu present. To combat this you have to go down a different route. Since the preference options are simply saved in a file, we can edit this file and adjust the results as needed. You may need to delete preferences if you know (for certain) that something is wrong, or you have added an incorrect preference file and want to remove it. Most incorrect preference files usually get removed after a while, however its worth making sure.
To delete the preference file open up Finder and find the following path:
/Users/[name]/Library/Application Support/Firefox/Profiles/[random letters].default
This stores a lot of your preferences and related files that Firefox uses. Within this list find a file called “pref.js” and open it in TextEdit or your favourite text editor.
Within this file you will find all of the user preferences that you set (not ones by the application itself, these are stored elsewhere). They take the format of:
Look through the list and find the preference file you have added. To remove it, simply remove the line that the preference occupies. Save the file and restart Firefox. The changes should take effect and not be present when you type about:config in the address bar.
Its a simple tip, however I have used it once or twice when I want to delete a preference that I have added. If you have any more Firefox tips, please leave a comment below.