YouTube Player Counter by Eppc

YT Player Counter is a simple Firefox extension that adds a small counter in the top-right corner of the YouTube player.
The counter can be easily controlled using your keyboard:

G — increase the counter (for example: number of correct answers)

Z — reset the counter

H — decrease the counter

The counter is not visible by default — you enable it by clicking the extension icon in the Firefox toolbar.
It works both in fullscreen mode and in the mini-player on YouTube.

Useful for things like:

Keeping score during video quizzes

Tracking correct and incorrect answers

Marking challenges and milestones while watching a video

How to use:

Open YouTube and start playing any video

Click the extension icon to enable the counter

Use the G and H keys to increase/decrease the counter
— Press Z to reset

Click the extension icon again to turn the counter off