>For example, on Firefox/Chrome "right click > search on google" open a new tab, on Opera it load Google in the current tab.
Uncheck Preferences-Advanced-Tabs-"Reuse current tab".
>on Firefox/Chrome middle-clicking on the back button open the previous page in a new tab.
You can clone tab, so it's possible to implement clone tab and go back macros with custom button like opera:/button/Duplicate%20page,,,%22Back%20in%20background%22,Rewind%20&%20Back
Uncheck Preferences-Advanced-Tabs-"Reuse current tab".
>on Firefox/Chrome middle-clicking on the back button open the previous page in a new tab.
You can clone tab, so it's possible to implement clone tab and go back macros with custom button like opera:/button/Duplicate%20page,,,%22Back%20in%20background%22,Rewind%20&%20Back