Ok - so - the API string in buster is actually:
$ rgrep "2\.4"
dav/content/provider.js: static getApiVersion() { return "2.4"; }
eas/content/provider.js: static getApiVersion() { return "Beta 2.4"; }
dpkg/content/tbsync.jsm: apiVersion: "Beta 2.4",
So now EAS complains for me :-) But since I don't need that, I removed
it. But IMHO neither webext-eas4tbsync nor webext-tbsync should be
"Beta". I guess it's fixed for sid, where webext-tbsync is newer and
webext-eas4tbsync got a "version bump to 2.4" in 1.20-2.
HTH
Jan-Marek