Developing browser extensions seems hard

I'm building myself a bookmarks/read-it-later website to replace Instapaper and one requirements is saving links to it via a browser extension. (I also need to write an iOS app but that's another kettle of fish). I didn't think it would be too bad: it's just JavaScript right? The problem lies in that there doesn't seem to be any form of intellisense for the WebExtensions API, so I have to spend…