I really like it, but the icon should have an alternative color when using the dark theme, since in the new Proton UI it is not much visible.

Thank you for re-instating this FF feature!

Invokable from page, link, and bookmark, but there is no way to refresh the sidebar and it’s not remembered over browser restarts

It is not working for me with bookmarks sidebar, no menu item. Is it possible to use it with Firefox about: pages?

Works well, but two changes would make it more useful:
1. Option for a sidebar home page so that, for example, a news site could appear when firefox is started rather than having to first right click a bookmark
2. Clicking a link would display in the main window rather than in the sidebar. So if I want more detail on a news story, I see it in its intended format and I don't loose the original content of the sidebar