Except for the annoying interaction (I think) with "open new tabs next to current tab", which causes Sideberry to somehow leave behind lots of stupid empty tabs named after the page the real new tab had. I deal with it, but it's annoying.
>>PaulDa+(OP)
Oh, I'm yet to hit that problem. My current annoyance is that sometimes it gets confused after Firefox restarts, and I end up with a flat dump of tabs + an unending spam of those tiny warning popups at the bottom of its UI. The few times that happened, I ended up restarting Firefox again to stop the warnings, and then rearranging the flat list of tabs into groups and panels I want them to be in. Fortunately, it's not that big of a chore.