Thanks a lot for taking the time to answer me. I really appreciate it.

Apparently on Firefox I have to give access to all websites when i want to use the Keychain extensions. Other browser might have the option to limit the access to certain sites though.

I usually don't have any extensions in my browser, so that's why I was so surprised that I need to allow that kind of access. I am most worried that an extension can spy on the data which I put into any website, something which seems to be possible. In the end, it comes down to whom we trust.

Again, thanks a lot for your work and your reply!