I'm not in KDE, I'm in Mate which has no such feature by default.
Thanks for the second tip, if I try Firefox again I'll do that. Is it possible to get auto-updates at browser shutdown or in the background, when it doesn't interrupt my flow? I would probably forget to ever update them if it's completely disabled...
* to disable addon auto-update check - about:addons > wrench: uncheck "update addons automatically"
With browsers I think it's easy to become entrenched; not that that's necessarily bad.