Does the webpage say anything about the extension being unavailable or something? I don't know if stable Firefox has that one enabled. I use Nightly which had allowed all extensions for a long time and idk about Stable
could be that, but all i see is the page with the big blue download button (which is slightly grayed out and not working) so idk. anyway, i found in this posts thread a good pdf reader so i wont need the browser extension, thanks though