Yes, it is about Bug 1609556 - Migrate toolbar-context-menu to Fluent (Firefox 78+)
comment this one below inside the addon
if (!FOX85 && appVersion >= 78 && url == "chrome://custombuttons/content/overlay.xul")
Shall consider to put the version 78 then
Still not looked, and still not going.
You please ask here, I do not watch others there.
So you ask about the version is impaired, sure indeed, no any version is complete paired, one most close is a javascript, but promise-resolvers thing from the 120 version for example. In all do not rely on the number.