> mbasic has been unmaintained for a while, in my experience.

true

> Lately, many links (e.g. group posts) point to m.facebook, which means that I just get redirected to the home page.

Conversely, in a browser without js, m.facebook.com redirects to mbasic

> You may need to access the page by clicking a link from another mbasic page in order to have some kind of checksum in the URL.

Good idea! From the main page with the feed, I can see the number of new messages but when I click on the link, I see an error message (same as with direct links).