I've been using Firefox since Windows first came out and NEVER had this problem (or any other) until about a month ago. After an update, my bookmarks sidebar failed to work. I tried to update again, but got the message "Secure Connection Failed". After many tries, I was able to load a 32 bit ( V 1390.1) which was offered from Mozilla. This despite the fact that my PC is a 64 bit machine. This 32 bit version works poorly! I've repeatedly tried to load a 64 bit version, hoping that it would work as Firefox has in the past. I am still getting the the message "Secure Connection Failed", Error Code Mozilla_pkix_error_key_pinning_failure. What is going on??? I like Firefox and I'm reluctant to change browsers, but it may become necessary. Operating systwm: windows 10. Bob N