hi TeHWooF, as far as i know middle-clicking the tab bar normally causes a new tab to be opened. maybe you have used an extension to tweak that behaviour in the past that stopped working now? if so, it would be best to report the issue to the addon's developer so that they can make the necessary adaptation.

Undo Closed Tabs Button {web link} Tired of going to History -> Recently Closed Tabs just to undo a closed tab? Then this extension is for you!

This extension allows you to undo closed tabs via a toolbar button or the right-click context menu.