You can use: https://addons.mozilla.org/en-US/firefox/addon/old-reddit-re...
or https://libredirect.github.io if you want Libreddit
My rule for reddit:
reddit: www -> old
Redirect: https://www.reddit.com/*
to: https://old.reddit.com/$1Also useful, for example, if you want to be the one in charge of whether your browser uses the desktop version of Wikipedia rather than the mobile one:
https://en.m.wikipedia.org -> https://en.wikipedia.org
Redirect: https://en.m.wikipedia.org(\/.\\*)?
to: https://en.wikipedia.org$1