About the issue
Starting in Firefox 40, Mozilla removed something called the “widget module” from Firefox. The 1Password 3 extension is old enough that it relied on the widget module, so it doesn’t work in Firefox 40 or later.
You’re only affected if you’re using the 1Password 3 extension in Firefox 40 or later.
If you’re using the 1Password 4 extension or later, and you don’t see the 1Password button in your browser’s toolbar, try these steps.
What you should do
To resolve the issue, switch to another supported browser or upgrade to the latest version of 1Password.