Hey, Stephan. Thank you so much for highlighting some pretty useful tools! I've now downloaded the word counter one (because I've been doing it as you said - going back a page after saving). And also the Medium Stories one because it does bug the hell out of me seeing my responses amongst my stories.
I would probably add Grammarly! They have a good chrome extension too that which works alongside your writing (though I normally switch it off until I'm in editing mode).
[EDIT] The medium word counter extension doesn’t work, it’s apparently not been updated since 2014.