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.
With reflowing zoom, all elements get bigger, but lose their relative sizing; eg. sidebars will remain on the screen, taking up relatively more space than they usually would. With pinch zoom, all elements get bigger, and retain their relative sizing to each other.
Basically, reflowing zoom tries to fit everything into a smaller space, while pinch zoom expands everything equally.
I’ve rebound my ctrl+mousewheel to be pinch zoom. It’s much more what I want when trying to zoom a webpage.