In my case the issue is with Firefox 43 (64 bit edition), Windows 7 Enterprise (64 bit), trying to use 1Password 18.104.22.1682 in Demo mode against my Gmail account. It loads the username and advances to the password page, then does nothing. It never tries to enter the password, and I don't get any error message. I update the browser extension today.
@jcheyney: Sorry for the confusion! I've split you off into a separate discussion in the browser filling category of the forums, since it sounds like you're not having any trouble installing the extension at all. It sounds like you're just having trouble using it to log into Gmail.
To be clear, 1Password will not take any action on your behalf unless you tell it to. So what it sounds like you're saying is happening is that you selected the Gmail login, and 1Password took you to that page and filled it. But 1Password isn't going to do anything with the next page (or any after that) unless you command it. There are a few ways to accomplish this:
I hope this helps. Please let me know if you have any questions