ProtonDB for Steam от Software Fusion

IMPORTANT
This extension uses manifest v3. To work, this extension NEEDS access to protondb.com and store.steampowered.com. We use this access to check the app's proton rating and display it on the website. Nothing more. However, in V3, firefox treats these permissions as optional and thus won't work by default. To fix this, after installation turn on the 'optional' permissions in the addon tab. Check this support page for more information.

ProtonDB for Steam adds proton badges to the Steam game pages.
This way, you know how well a game runs on Linux before you actually buy it.

The extensions shows you the proton rating, if available, and also if a game has a native Linux version alongside it.

The project is open-source and can be found on GitHub.
Credits to MostwantedRBX on GitHub for founding the project