I upgraded last week so my issue iOS not directly related to the upgrade but of course my Mac may have applied system data files and security updates overnight. Is there a way to tell?
All was well yesterday, this morning the extension has just disappeared, no sign of it whatsoever.
This terminal command has restored normal service (after quitting 1Password and opening it again)
/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -f -R /Applications/Safari.app
Very odd........
