In recent days Mozilla has begun activating Wayland support by default on Firefox Nightly for configurations capable of running Wayland.
Mozilla tweeted a notice that “Wayland was activated by default on Firefox Nightly (only) for eligible configurations last week.“
They encourage those Firefox Linux users on Wayland to check this bug ticket and connected dependent tickets regarding the Wayland port for known issues. There have been recent new bugs submitted around crashes, WM_CLASS handling changes, dragging tabs sometimes freezing Firefox, and menu alignment issues.
Confirmation whether you are using Firefox’s native Wayland support can be found via about:support.