What is it with Firefox’s developers these days? Every other release of Firefox seems to overwrite at least one existing setting … with a broken feature.
Firefox version 22.0 disables your PDF viewer and replaces it with a non-working proprietary viewer from Mozilla
Cure is quick:
Note: this works because “always ask” is less annoying than it sounds. It merely means “let me open it or save it”, and it will use whichever viewer you last used. On OS X that – out of the box! – means the system PDF viewer. Which works perfectly on everything except bizarro-interactive-secure-encrypted Adobe docs/em>