So Firefox 48 is starting to roll out e10s for end users. When e10s is enabled the 1P browser extension for FF no longer works. This is a known issues at least for over 2 years as of this post:
What's the current status as this will be the default in FF.
1Password Version: 6.3.1
Extension Version: 4.5.8
OS Version: 10.11.6
Sync Type: -