[fbcpck]

Not OP, but I decided to switch to Tampermonkey after GM version 4 which broke almost all my scripts due to the GM_## api changes. I no longer remember the exact details but it was poorly executed/communicated, and it’s easier to switch to TM instead of updating all the scripts.

The dashboard interface in TM is a lot nicer than GM too

[aepiepaey]

When Firefox stopped supporting legacy extensions, the Greasmonkey developers saw that as a chance to redesign their API (to use promises).

Tampermonkey used to be open source, but unfortunately isn't any more. I still use it though, as it has better UX (e.g. nicer dashboard, prefills @match when creating new scripts, better editor, etc).

An alternative to Tampermonkey that is open source and still uses the old style of user scripts is Violentmonkey (which also lacks in the UX department, if i recall correctly).