I walked into this trap yesterday as well. The reason being, they also changed many of my settings regarding application handling. While before that change, it

I walked into this trap yesterday as well. The reason being, they also changed many of my settings regarding application handling. While before that change, it was "Always ask" across the board, after the update, many file types were set to "Save File". So in addition to the about:config setting you should also check what is set for specific file types and revert that to "Always Ask". This is the kind of change, if there were competition, I would have stopped using Firefox for good.