I will often open up a page with a lot of links, e.g. Feedly to read the news, and as I scroll down the page, I like to use ⌘+click to open the links in a new tab.
With Firefox, the default behaviour out-of-the-box is that if you’re holding down the ⌘ key and you scroll the page with the scroll-wheel on the mouse, then instead of scrolling, it zooms the page in and out. This is never what I want.
To change this, type in about:config in the address bar and then search for the setting mousewheel.with_meta.action
The default value of this is 3 - which means if you’re holding down the meta (Command) key and you use the mouse wheel, it zooms the page.
Other valid values are 0 (do nothing), 1 (scroll normally - this is what I set it to), and 2 (go backwards and forwards in your browsing history)
Change the value from 3 to 1 and you’re set to scroll.
There is also another setting for mousewheel.with_control.action – if you’re on Windows and using Ctrl+click to open links in a new tab, then you’ll need to set this to 1 so that it scrolls instead of zooms when holding down the Ctrl key.