The recent update to Firefox 57 marked my favourite Tab Groups extension obsolete; the Firefox Multi-Account Containers extension it offers is nowhere near adequate - this apparent beta can't even move tabs between groups. (On the positive side, the new rendering engine fixes performance issues added two releases ago.) I'm trying to rig up a temporary solution in a hope they will do something about this one too eventually.
What I currently settled on is the Tree Style Tab extension combined with a set of silly local pages of the following form used as group roots:
<!DOCTYPE html>
<html>
<title>Group Name</title>
<body></body>
</html>
However, I can't find a way to protect them from accidental closing. Tried pinning them, but a pinned tab cannot have children. Even worse, a closed parent tab also closes its children with no way to restore them all at once. Any suggestions?