Thanks, very glad to hear it's useful! I can't reproduce what you're seeing, however; can you please say more about how you are clearing cache? I've updated Firefox to v66, tried clearing cache manually and setting it to clear automatically on exit, and can't get the install confirmation page to show up.

Edited again: fix should be in with 4.0.77. Please have a look?

Edited again: sorry, had to bump this back one version for the 4.0.76 bug fix.

Edit: got it. We need to be smarter about recognizing new installs. We'll have this fixed by our next update; very sorry for the trouble!