Can't uncheck "disable extensions" in Safari Develop menu After upgrading to macOS 10.13.4 my extensions in Safari were disabled. Safari Preferences Extensions tab says "Extensions can be enabled in the Develop Menu". However when I try to uncheck "disable extensions" in the Developer menu nothing happens and it stays checked.
This worked for me on Safari 11--> bottom of developer menu there is "allow unsigned extensions" click that;  Now go back to the developer menu and click disable extensions...