This is a great example of the challenges browser developers face: when something breaks, people often blame the browser since that's the thing they remember most recently changing but it's far more often that it's something the remote website pushed out which isn't visible to the user.
I don't blame Firefox here though I do believe this was a change to perhaps the strictness or level of introspection. I've observed two websites with similar issues.
Either way, I'm a-ok with these types of changes even at the expense of my time in remembering the cause and the solution.
Yes — I just find it an interesting challenge for even an experienced technical user to localize the cause of a problem like this. Visibility is important and I really like the way rapid releases have helped the web but it also sets you up to be the initial suspect.
