I have now tested it with Firefox and Violentmonkey, and the problem you are seeing happens for me as well. It seems that Violentmonkey is unable to inject the scripts in page context and instead has to fall back to content context. Open Framework requires the scripts to be injected in page context, otherwise it doesn’t work.
I don’t know why Firefox+Violentmonkey stopped working, maybe one of them released an update that breaks the page injection. Maybe it will get fixed in the future, maybe not.
You said that it works if you try it with Tampermonkey instead – can you just switch to Tampermonkey altogether, or is there a problem with this solution?