1) Yes, flash causes a lot of crashes. However, it's also the only plugin that is used every day by pretty much everyone and interacts with pretty complex material (video, simple interactive material). Suprise?
2) HTML 5 is great, but not ready for prime time yet. Full screen support is botched at best, the debate about which video standard to use caused a huge delay and scared of many potential adopters and support isn't yet widespread.
3) Adobe turned Flash Player into a safety leak that uses more system resources than it should (one of the few things I agree with Steve Jobs on), but version 10.1 and especially 10.2/10.3 changed everything. Pretty good hardware support and increased stability made Flash worth using again.
4) What's wrong with Mozilla these days? They bash pretty much everyone. Opera does it too, but in a more constructive and rational manner. Those guys at Mozilla are sure having a hard time. Not that long ago, IE was junk, Opera was nigh unknown and Chrome didn't exist yet. Safari for windows was and still is a joke. FF was the only browser that had mass market appeal and was a quality product. Today, IE is fast and secure, Opera is still the great guy that everyone forgets about and Chrome is gaining market share faster than you can speak.
Time to release a better browser....