Once I enter responsive design mode, the 1P extension will no longer fill in fields.
1Password Version: 6.8.4Extension Version: 126.96.36.199OS Version: macOS 10.13.1Sync Type: Not ProvidedReferrer: forum-search:firefox responsive design mode
There does seem to be a bug. It isn't clear precisely where or why yet so we'll need to investigate. Thank you for bringing this to our attention.