Google search criteria can't be edited in Safari
I've got a 2015 MB Pro running OS X El Capitan version 10.11.12. My default search engine is Google. After the recent update, whenever I search something in the Apple search bar in Safari, it will bring me to the Google results page like normal, but if I want to edit the search criteria in the Google search bar (not the Apple search bar), it won't let me. It won't delete, add or amend the search criteria in the Google search bar within the webpage.
I've tried Yahoo and Bing and both work fine. I've also tried Google on Firefox and it works fine too, so it must be something with Safari.
Any suggestions? Anyone else have this issue?
MacBook Pro (Retina, 15-inch, Mid 2015), OS X El Capitan (10.11.2)