Mozilla is reminding Firefox users that a necessary root certificate expires soon and that older browser versions could become a security and usability nightmare in a few months. Starting March 14, 2025, Firefox versions older than 128 (ESR 115.13) containing the expired certificate will likely cause “significant” issues with add-ons, content signing, and streaming of DRM-protected media.
Users advise Mozilla to stop making unwanted changes to the Firefox UI while simultaneously reducing user options if they want people to update.
Most can be disabled. Mine looks pretty much the same as it did 5 years ago. Try installing the developer edition or nightly to test if you can edit it to your liking