The Windows panel in the Opera browser is a convenient built-in replacement for the tab bar. In the Windows operating systems, middle-clicking a tab in the Windows panel will close it, but in Opera for Linux and Unix, doing so will just duplicate the tab, which is annoying in my opinion.
However there is a way to restore the behavior we can see on Opera for Windows:
- Go to the Tools > Preferences menu
- Click on the Advanced tab
- Click on the Shorcuts item in the left panel
- In the Mouse Settings, double-click on Opera Standard
- Click on Windows Panel
- Click on the New button
- In the left part of the new shortcut, type Button3
- In the right part of the newly created shortcut, type Close page
- Save and close all the dialogs
You can now close the tabs by selecting them and middle-clicking them!