There's a convenient way to install plugins but it's not mentioned anywhere?
I accidentally drag the url of the .xpi file to the Add-ons Manager windows and it did work.
Video for illustration: https://imgur.com/15PAZwT
The url in in this Release Page https://github.com/bwiernik/zotero-shortdoi/releases/tag/v1.4.2
Video for illustration: https://imgur.com/15PAZwT
The url in in this Release Page https://github.com/bwiernik/zotero-shortdoi/releases/tag/v1.4.2