Apart from the major version number change, Firefox 100 comes with GTK overlay scrollbars enabled by default so they won’t take up space when you’re browsing the Internet and also to make the open-source web browser look more modern.
On Linux, users will be able to enable or disable the GTK overlay scrollbars via the new “Always show scrollbars” options implemented in the Browsing section under Settings > General. By default, the option is disabled, which means that the GTK overlay scrollbars are enabled.