Compatible Firefox forks with Native Windows Titlebars support
As of Mozilla Firefox 128 ESR on Windows, Native Windows Titlebars support is no longer available in Firefox and most of its forks.
If you have been directed to this page by a notification banner in Geckium, it means your installation of Firefox has been updated to 128 ESR or newer, meaning it can no longer be patched for Native Windows Titlebars. To continue using Native Windows Titlebars, you can switch to one of the following forks:
Marble is a fork of the latest Firefox for Windows, it is currently in Beta. It adds Native Controls (such as native titlebar (Aero), and some other controls), not to be mistaken with old Windows support.
https://github.com/Erizur/marble/releases
An unnamed Generic Firefox fork for Windows 7 that adds Native Controls (such as native titlebar (Aero), and some other controls), as well as restoring support for Windows 7 and even Windows Vista.
https://github.com/e3kskoy7wqk/Firefox-for-windows-7/releases
While it cannot on Windows, Mozilla Firefox still supports Native Titlebars on Linux! Pair it with https://gitgud.io/wackyideas/aerothemeplasma and you can get the full AERO look for Mozilla Firefox that you are most likely trying to achieve.
For new users, a good starting point may be Kubuntu, the official sibling of Canonical Ubuntu featuring the KDE Plasma Desktop Environment (the Desktop used by Valve's Steam OS), but for the look in this image you can go with any Linux Operating System you would like AS LONG AS it comes with KDE Plasma.
More browsers may be added to this list as they are released.