Hi there! In youtube I need to press refresh to get the extension to work. There is like a quick flash at the search bar while pressing ctrl+y before refreshing the page.
We'll probably need to wait until January 29 for Firefox 66 to be available in Developer version, so as to start using the fix to https://bugzilla.mozilla.org/show_bug.cgi?id=1303384, which allows the user to register keys in a non-conflicting way. Firefox 66 won't be availabe to users until late March though.