Windows from Firefox 134 using either hardware (on devices that support it, where the range is the same as Edge) or software (on Windows the user must pay for and install an extension)
macOS from Firefox 136 using either hardware or software.
Linux from Firefox 137 using either hardware or software (via the system ffmpeg).
Mozilla Web Developer Docs
Is this what you talking about?
Huh, I didn’t realize they finally snuck that in. I’ve been using Edge as a workaround for a long time. Thanks!