After updating should be opened options page with notice about limitations:
https://github.com/Infocatcher/Right_Links_WE/blob/0.5b8/_locales/en/messages.json#L21
And with links to legacy version.

Also I don't know, what is better: show available update to features-limited WebExtension version for users, that still use old Firefox (and wait for extension update) or limit minimum version to Firefox 57 (but actually works at least in Firefox 52 ESR).