Great extension! This and the KDE Connect app are two really useful integrations.

It's been annoying me since switching to Firefox that there's no download progress indication by default, without separately opening the download manager. I've tried other plugins that add a Chrome-like downloads bar to the bottom of the window but they're just not very good.

Then I just happened to stumble onto this Plasma integration plugin and voila, downloads now pop up a proper download status in Plasma itself! Fantastic!