Nie działa z kontenerami.

Very promising! But the order of the tabs is revers!

When you go Right+Clicking on a Bookmarks folder, Firefox 57 opens the tabs and the *default* order is as following: the tabs are arranged left to right, same order as the bookmarks in the folder from top to bottom (top bookmark is leftmost tab just opened; bottom bookmark in that folder is the rightmost tab opened).
Unfortunately your extension causes a reverse arrangement! Not only in your extension but also in the Bookmarks folder when you open a Bookmarks folder as "Open all in tabs". The tabs are arranged right to left (top bookmark is rightmost).

Could you please reverse the order?

This is great replace for tab group. Very Thx
if it's like a tab group it's 5 stars

Pretty great, but I noticed two bugs. You can't seem to create new tab sessions when using the sidebar. Entering a name in the textbox and pushing the "+" button just doesn't seem to do anything, but only in the sidebar interface, works fine from the toolbar. Secondly if you move the toolbar Tabber button into the Overflow Menu, when you click on it in the Overflow Menu, the Tabber interface is too wide for the Overflow menu.

Like it so far. Could be more compact and customizable.