Just want to add that I updated my MacOS to the latest update 10.14.3 and Firefox to 65 and now 1Password does not work at all in Firefox. I usually use the CMD \ to autofill a password and the app does not respond. If I click the 1Password icon in the browser, the app does not respond.
I've split your comment away from the 1Password X thread because if you use ⌘\ to fill then you're using our companion extension. 1Password X is a standalone extension and it doesn't support that keyboard shortcut.
There's a number of possible reasons why things aren't working and a diagnostic report is the best way to identify the cause. Can you create one for me please and send it in. This link will guide you through the steps and has sections for the various supported versions of 1Password.
How to send a 1Password diagnostics report
Please do not post your Diagnostics Report in the forums
The email address you will want to use is [email protected].
Once you've sent the report you should received an automated response from us with a ticket ID. If you can post that ticket ID here it will help us locate your diagnostic report and we'll see what it reveals.
If after clicking the Create New Mail Message... button in the diagnostic reporting tool you see a bunch of errors dismiss the error message and instead now click on the icon to the right. This will open a Finder window focussed on a folder titled Diagnostics. In there you will see a folder and a ZIP file (whose contents are the folder). Attach the ZIP file to your email and send that in.