I cleared the cache and restarted Firefox.
With the Network Tab open I create a new Simple Page. On Save&Continue the error message Failed to save the page. Reason: Server not responding appears and one line is added to the Network Tab showing the error error xhr ‘Mixed Block’ .
Similarly on the chrome browser and I get the same result. The Network Tab shows
Status = blocked:mixed-content
Type = xhr
Initiator = prototype.js:1745