
Rename the ''mimetypes.rdf'' file to ''mimetypes.old'' and then restart Firefox.

See the article ] for more information, such as where to find the folder when Firefox is not open. * In the page that opens, click the "Show Folder" button ** Go to Help (or ] > ]) > Troubleshooting Information ** Enter '''about:support''' in your address bar and press enter * Go to your Troubleshooting page, either: Hopefully when that happens, it will default so that PDFs will open in Firefox. Try renaming your ''mimetypes.rdf'' file in your profile folder - this file is where the file actions are stored so when it is missing, Firefox will recreate it. Read this answer in context 👍 3 All Replies (4)

To go to your profile folder if Firefox is open: Try renaming your mimetypes.rdf file in your profile folder - this file is where the file actions are stored so when it is missing, Firefox will recreate it.
