Hi, Thanks for your feature request.
This looks like a duplicate of https://forum.vivaldi.net/topic/46811/quick-unit-converter-currency-time-zone-temp-scales-measurements-oz-cm-etc Please vote & discuss at that thread, thank you.
You can use the forum search first to see if you can find similar requests. If that doesn't work, I've catalogued all the requests here.
@hyfrehyfre The original menu is for tabs, so it wouldn't be possible to just "move" it to the context menu. It would be possible to do this via a mod or an extension, I suspect, if you want to ask someone in those sub-forums to help.