Hi @Jakub Chodorowicz 
Basically, if a browser extension blocks Miro, we can only suggest that you switch it off. Thanks for your understanding!

I had this problem as well, I only use the Testing Playground extension for my local development. So I’ve added that URL to the Site access settings of the extension. I don’t care about any other websites to load this extension. In this way you don’t have to switch the extension off and on over and over again.

Good workaround. Another option is change the Site Access to On click. I don’t need Testing Playground being loaded on every page automatically.