Hello fellow dex user. I had the same experience with firefox and discovered a "solution" - DEX developer mode [1].
Yeah, zooming is a fucking mess. To zoom in firefox, doubleclick the mouse, and while HOLDING ON THE SECOND CLICK you can move the mouse up and down to zoom. Neither control +/- and control + scroll wheel work.
Selecting text: click on a word and hold the mouse button down. This works exactly like long-pressing on a touchscreen and getting the text select pop-up.
Yeah, zooming is a fucking mess. To zoom in firefox, doubleclick the mouse, and while HOLDING ON THE SECOND CLICK you can move the mouse up and down to zoom. Neither control +/- and control + scroll wheel work.
Selecting text: click on a word and hold the mouse button down. This works exactly like long-pressing on a touchscreen and getting the text select pop-up.
[1] https://forum.xda-developers.com/galaxy-note-8/help/firefox-...