Hi there! A good idea, a very good one actually but maybe because people need to see it work across several sites. I'll give you a few to start off with, based on where I've played dice or know dice is popular:

1. Crypto.games
2. Bitsler
3. Bitvest
4. 999dice
5. Fairlay
6. Yolodice
7. Freebitco.in

It could be tricky but if you could really interface with regular casino software:
1. Sportsbet
2. FortuneJack
3. Bitcasino
4. Bitcoinrush
5. Betcoin

Get your code open source too. And have as much detail as possible for a newbie to understand how your extension verifies provably fair (maybe even a tutorial inside to teach them) and you might have something on your hands. Don't worry, new extensions will be difficult to break through as people rightly won't trust it. Maybe work with a couple of owners to suggest your extension.

It sounds like a cool thing, but perhaps one of the reasons people don't check it out is the same I have: I am very cautious when it comes to crypto browser extensions because the risk of it being something that scams you just seems too high. Okay, you've shown the demo which looks cool. But I am sure you understand that it doesn't prove that the extension doesn't do anything additionally, such as, say, get the money out of the casino account when a person is logged in and checking if the bet was fair. If you find a way to show that it's safe to use the extension, I am sure it will help make it more popular. Good luck!