For me, Firefox in its default layout is barely legible, because everything is too small. I could use the zoom function, but it only zooms the content of a page, not the rest (tabs’ text, search bar, icons…)

To make the whole of Firefox bigger, look for layout.css.dev in about:config and set it to true, then change the value of layout.css.devPixelsPerPx to something bigger than 1. I chose 1.50.

(edited on 14 december 2025 as Firefox changed things a little. This information is current as of Firefox version 146.0.)