Arrow keys don't work on FF macOS

[Sv443]

On Firefox in macOS, pressing arrow keys to skip forwards & backwards doesn't work and comes up with this error:

Update:

The problem comes from the window object being only limitedly available in userscripts. YTM needs certain properties that are unavailable regularly, thus unsafeWindow is required to dispatch the arrow key events correctly.
This problem also extends beyond just the "arrow key skip" feature and applies to a few other BetterYTM features.

In the current constellation I don't see a way for this to be a potential vulnerability, unless a malicious, non-vetted plugin or userscript is installed, so this is just how it's gonna have to be.
You may remove the @grant unsafeWindow line in the userscript header but note that all features that dispatch events might break and you will be unable to use any BetterYTM plugins.