Check my setup below. (I added the browser version just for you^^)
Make the browser to your standard browser.
Open 1Password Application and click on a url.
The browser opens a page like https://discussions.agilebits.com/?onepasswdfill=xxxx&onepasswdvault=yyyy
The issue is that the site doesn't even load, it's just a empty white space. When I remove the onepasswdfill parameter it loads again.
1Password Version: 6.6.407
Extension Version: 4.6.5.b2
OS Version: Windows 10 Insider Preview Build 16184
Browser Version: Firefox Nightly 55
Sync Type: 1Password Accounts