Disclaimer: Not talking about Ctrl + Scroll.

I tried the Mouse Pinch-To-Zoom extension, which is buggy on some sites. And I even bought a physical touchpad for pinch zoom. Today I just leaned that it’s natively supported as an experiment feature by FireFox

There are specific actions defined to set what happens if you rotate the mouse wheel and hold down modifier keys like Alt or Ctrl or Shift. You can disable this action by setting the related mousewheel pref to 0 (zero) on the about:config page.

mousewheel.with_alt.action = 0 

0: Nothing happens
1: Scrolling contents
2: Go back or go forward, in your history
3: Zoom in or out (reflowing zoom)
4: Treat vertical wheel as horizontal scroll
5: Zoom in or out (pinch zoom)

I changed the value to 5, and it works perfectly.