There are some legacy users out there and there are software adapted to the PowerPC Macs that Mozilla has given up on a long time ago.
There is a Firefox browser implementation called TenFourFox which runs on the PowePC G3, G4 and G5 Macs.
It might be worth considering for those die hard legacy users but the legacy 1Password Extension is unlikely to work on the Firefox 45 ESR that this browser is based on.
Plus the 1Password 1 and 2 versions aren't even downloadable from Agilebits servers currently.
1Password Version: Not Provided
Extension Version: Not Provided
OS Version: Not Provided
Sync Type: Not Provided