Yes. I use a FireFox extension called ViolentMonkey that allows you to install scripts.

There is a script called Simple YouTube Age Restriction Bypass: https://github.com/zerodytrash/Simple-YouTube-Age-Restriction-Bypass?tab=readme-ov-file

Install the script in Violent Monkey and you should be all set to watch age restricted videos in Firefox without signing in.

I know of this userscrpit, worked fine for me the last time i came across something age restricted

Isnt this possible with Grayjay, or do you still need an account?