So I am running El Capitan (just upgraded), with 1Password 5, and Firefox ESR 38.3.0 and I am getting a message that the 1Password Firefox browser extension is incompatible, when I try to load it by clicking on Install Browser Extension in 1Password. What am I missing? How do I fix this?
Firefox 38 doesn't support the latest version of 1Password's extension, so you'll need to grab version 4.4.2. That should get things up and running nicely. If you have any other questions, feel free to let us know.