How to restore rectangular UI elements in Firefox

23 Oct 2026 it Table of Contents Preparations Purging roundness from the browser Fix toolbar buttons shape Fix menus shape Eliminate round corners for a lot of things Rectangle Quit dialog Rectangle UI controls Rectangle new tab Other customizations Borders around URL input bar and buttons Remove unnecessary gap on the bottom of tabs Changing the accent color Notes After recent update of Firefox, I found that it's designers done useless changes for the UI elements … again. With this update every control and shape in the browser lost its' corners for unknown reasons — maybe it is just a new trend in the UI design, considered cool because of made up reasons. I don't know. But I know the next: I hate made up unnecessary changes in the UI of programs I'm using. And also I hate rounded corners, considering them ugly. Figure 1: New and ugly Firefox interface Luckily, Firefox developers still doesn't remove the option to customize the browser look&feel with the help of CSS. So, it is…