Hi, I'm very sorry to hear that the extension is not working for you. It may be that another extension is interfering with it's functionality, a known example would be Tampermonkey with scripts that run on YouTube. Please also make sure that your browser is up-to-date, as the extension will only work with Firefox 109 upwards.
If you want to find the root of your issue, feel free to open an issue on the project's GitHub page, and we can work towards finding a solution: https://github.com/NikkelM/Random-YouTube-Video/issues