1Password Extension Version 3 Not Syncing with Application on Firefox [Fixed by resetting db in FF]

I was having a problem with a conflict between v3 and v4 of the 1Password extension on Firefox, but I fixed that by removing v4 and disabling extension sync. Now, v3 runs fine, but it's using an old version of my database. When I open the 1Password Windows app and examine its data, it appears to be up-to-date, but these data are not making their way to the extension. I've tried restarting and removing and reinstalling the plugin, but all to no love. How can I force the plugin's data cache to flush or somesuch?