The Mozilla developers have chosen not to remove the compact panel display mode and continue to ship the functionality associated with it. In this case, the user-visible setting for selecting the panel mode (hamburger menu in the panel -> Customize -> Density -> Compact or Personalization -> Icons -> Compact) will be removed by default. To return the setting to about:config, the "browser.compactmode.show" parameter will appear, returning the button for activating the compact mode, but with a note that it is not officially supported. For users who have compact mode enabled, the option will be enabled automatically.
The change will be implemented in the May 89 release of Firefox 18, which is also scheduled to include an updated look and feel developed by the Proton project. As a reminder, compact mode uses smaller buttons and removes extra space around panel elements and the tab area to free up additional vertical space for content. The mode was planned to be removed due to the desire to simplify the interface and offer a design that would suit most users.
Additionally, Firefox 88, scheduled for April 20th, is expected to enable WebRender for all Linux users, including Xfce and KDE desktops, all Mesa versions, and systems with NVIDIA drivers (previously, webRender was only enabled for GNOME with Intel and AMD). WebRender is written in Rust and allows you to achieve a significant increase in rendering speed and reduce CPU load by offloading page content rendering operations to the GPU side, which are implemented through GPU-executed shaders. To force enable in about:config, activate the "gfx.webrender.enabled" setting or start Firefox with the MOZ_WEBRENDER=1 environment variable set.
Source: opennet.ru