I agree with appel and I learned today that Adobe is going to stop supporting Flash on GNU Linux
They haven't dropped support for Linux (despite the sensationalist news headlines on some websites), they've just decided to drop support for the old and rather ancient NPAPI (Netscape!!! Plugin Application Programming Interface). They've instead decided to move to the better Pepper API (PPAPI).
"a set of modifications to NPAPI to make plugins more portable and more secure". The modifications are designed specifically to ease the implementation of out-of-process plugin execution. Further, the goals of the project are to provide a framework for making plugins fully cross-platform
Although not supported by Firefox, Opera and Safari atm (IE's mostly always had its own weird thing), its an open standard that can easily be implemented if so desired. If a major plugin like Flash makes this move maybe other browsers will think about supporting it otherwise you'll end up with a chicken and egg situation and we could be stuck with NPAPI for a long long time.
In the long run its a superior choice over NPAPI and much securer (plugin's are a major security hole). Its something the Java Plugin should consider too. However the biggest win (especially for a company like Adobe who doesn't have unlimited resources for every platform) is once you write the plugin for one platform its much easier to port between others, so in the long run it can be better for Linux which has been neglected by plugin makers for years (especially Adobe).