Unfortunately this extension doesn't work. At the moment, all it does when clicked is display a sort of credits popup, and it doesn't insert anything onto the workout page. It *does* insert an *import* button on the workout list, but this button doesn't work, even with workouts downloaded through a working Chromium extension.

I'm already using the extension on chrome and as I am a regular firefox user, i wanted to switch but I couldn't make it work.
There is no "download" button in the workout page.
The "Import workout" button is present though but I tried to import a workout (downloaded with the chrome extension, .json file) and nothing happens...

Edit : thanks for updating, I can now download a json file but trying to import it leads to an error "Failed to import training. Try again". I compared both chrome and firefox downloaded files and they are exactly the same.