Firefox default zoom factor too big? Solution! I installed Firefox and Chrome on a new laptop with a 1920x1080 resolution. Everything looked fine in Chrome, but the makers of Firefox thought it would be a good idea to make things bigger! In addition to larger text, the graphics looked blurry, and some were cut off on the edges. This was due to the pixel density.
To solve this, type about:config into your Firefox address bar, go there, and confirm when it asks if you want to proceed. Then, start typing the following into the search bar, just below the address bar:
You can keep typing that in until only one option is left, or you can stop typing early and find it in the list. The default value in my case was -1.0, so I changed it to 1 and that fixed it.
Here's a video that shows the process, in case you need help. Note: You need to right-click on the option you want to change to get the little menu to pop up, then choose "Modify".