I find most implementations of this jumpy and distracting - just too eager. Often I'm scrolling up to reread the top line of text. Then the bar pops up and blocks my text, it is daft!

Awesome, thanks! Trying it; I've been thinking of building something similar for a few weeks. Site-specific (like the Medium addon we're discussing here, or domain-based userContent.css) solutions suck, I want something generic (like the bookmarklet) and automatic (thus the "tradeoff" of popping the dickbars on under certain conditions, like you did when scrolling up).

Ever thought of packaging this as a Firefox/Chrome (WebExtensions) addon? Want to collaborate on one? Or if you don't care, are you okay for me to start one from your userscript?