I am trying to install Video DownloadHelper on Firefox on a MacBook Pro 10.15.7 Catalina. Clicking on 'Download,' I get 'video_downloadhelper-4-9-22-fx-sm.xpi' And a message saying 'There is no application set up to open the document...' It says to search the App Store - but there is nothing. I have changed .xpi to .zip - but no luck. How do I install Video DownloadHelper on my MacBook Pro running Firefox?
If you saved the xpi file to your computer, you can install the add-on using the gear icon in the upper-right area of the Add-on Manager Extensions panel. Go to about:addons -> Extensions, select Install Add-on from file... from the gear menu, then find and select the file.