I'm using a friends computer today. When you select any link in the Google search results it opens the link, in the same tab, but the Firefox browser's back button is grey. I checked the history, and the Google search is there, as the previous page. A complete Malwarebytes scan is negative. All add-ons are disabled. (I disabled them.)
This problem apparently only occurs on the Google search results page. The back button is working correctly on the other sites I've tried.
Firefox Quantum 61. Windows 8.