This is huge news! Adobe has just contributed the virtual machine running in Flash Player 9 to be Mozilla’s implementation of ECMAScript 4. Read Tinic Uro’s announcement here or the story on CNN here.
What an enormous and generous contribution! Macromedia, and then Adobe, surely spent thousands of developer-hours on this VM. Beyond that, it is fully tested, optimized, and proven by its real-world use in Flash 9 and Flex 2 apps. Adobe well deserves a round of applause for giving it to the open-source Mozilla project, and hopefully both products will be bettered by their common codebase.
Furthermore, Adobe is committing to a continued relationship with the Mozilla project:
Adobe has a dedicated team for this open source project, including Dan Smith, module owner, and Jeff Dyer and Edwin Smith — Adobe engineers who worked on the original source code. Contributions to the Tamarin effort will be managed by a governing body of developers from both Adobe and Mozilla.
This is taken from a good FAQ hosted at mozilla.org which might clear up a few questions.