Love the extension, does a lot of stuff that enhances my YouTube experience. So thanks for whatever led to that point.
Here comes the "But - instead of shying away people blatantly that are coming to your website with this:

"To get in touch with me send your message directly to webmaster@mrfdev.com and if you're lucky you'll get a reply.
Don't send feature requests, I ain't got time to implement new features."

These people are trying to help you with ideas of new features, which will make your work even more renowned. So turn the approach around. Give the possibility to donate 5 bucks and by that give me the chance for a submission. Nipping ideas in the bud is the wrong mindset.