Just did a quick update to the add on, mainly to be able to quickly enable it and disable it, just clicking an icon in the URL bar.
https://addons.mozilla.org/en-US/firefox/addon/reddit-to-wayback-machine/
Also open sourced it
https://github.com/pe1uca/reddit_wbm/releases/tag/v2.0.0
You can read the code and the feature being used, which even if you see the url displayed, internally the request never leaves your browser.
https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/webRequest
That’s great! Thank you