This is something originally from Opera many years ago and is in Vivaldi browser today. i would love to see it in DOpus as well:
Holding down the right mouse button and clicking the left button is the equivalent to pressing the back button. Holding down the left button and clicking the right button is the equivalent to pressing the forward button.
Most mice have dedicated back and forward buttons these days?
The more expensive ones do, but certainly not most of them.
It used to be referred to as a 'chord' and you either used the mouse software (like mouseware, or the logitech mouse control panel) to convert it to an action (like back/forward/open email etc)
To do chording in apps which dont natively support them, I use autohotkey
if you need a mouse gestures program you can try StrokePlus.net, for mouse buttons simulated keystroke/cording/timed actions/etc per app you can try X-Mouse Button Control
