On the Add-ons page, you are able to Disable it but there's no Remove button? That's normal when extensions are installed in a "shared" location rather than in your personal Firefox settings folder. ''For quick reference, you can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:'' * Command+Shift+a (Windows: Ctrl+Shift+a) * "3-bar" menu button (or Tools menu) > Add-ons ''In the left column, click Extensions. Then your extensions are listed on the right side, enabled first, then disabled.'' If it's essential to completely remove it, maybe there is an option somewhere in Acrobat for that but, if not, you will need to figure out where it is on the system. This thread walks you through that process: [https://support.mozilla.org/questions/1113898 failing to remove a globally installed addon].