A website that I use at work all of the sudden started to render in a very broken way. Since we had had similar issues in the past I originally thought that it was a problem on the web application itself. However, after asking a co-worker I learned that the breakage is caused by a new feature that is enabled by default in Firefox 23: mixed content blocking. The feature is explained well at the following URL, but it basically boils down to “Firefox will block HTTP content referenced from a page served over HTTPS”.
The feature is a nice security feature. However, I think it has been terribly implemented in my opinion — first, you cannot create persistent exceptions (whitelist); second, you cannot create exceptions for entire domain (you have to create them on a page by page basis) so next time you open a page on the same site that also has mixed content then the mixed content will be blocked too. For the second issue, reading the comments in Mozilla bug 873349 is enlightening.
So, I can appreciate all the work the Mozilla developers have put into this feature but I have no option other than to disable it because it really puts a dent on my productivity. Let’s see if this feature is enhanced in a future Firefox release.