For Mac OS X, the default folder is located at:
For Windows 7, Windows 8, 8.1 and Windows 10, you can find your Firefox profile folder at: C:\Users\(username)\AppData\Roaming\Mozilla\Firefox\Profiles\faut. Click 'Add-ons.' You can also hold 'SHIFT' + 'COMMAND' + 'A. Click on the three lines in the upper-right corner to open a menu. It will open your specified folder in the Finder window. Browser plug-ins typically do not support all PDF. Installing Firefox 19 or later, for instance, can result in your Adobe plug-in being disabled and replaced.
