From Gnash Project Wiki
In Task #6588, I've been asked to create a section of the manual which describes how people can help. I'd like suggestions on things that people can do (details on how they can do it need not be added--if I have any questions on how people can accomplish the tasks I'll ask you for clarification). I suspect we are talking about people who aren't ready to dive in to the source code.
Testing is important, and it's the main thing non-programmers can help us with. Due to licensing issues we rely on other people to test our testcases with the commercial tools, and work with us until the problem is fixed. Producing simplified testcases that can easily reproduce the problem are are valuable part towards making Gnash compatible and fully functional.
- Run gnash test suite (make check) on different platforms/configurations and report the results.
- Create detailed bug reports when problems are found (instructions on what information to include for the best results should be included).
- Write SWF tests (with Ming and with other compilers), and test runners.
- Run the online testcases to catch eventual bugs in the tests themselves (follow instructions on that page).
- Pick one of the unfinished ActionScript classes that exist only as a stub (like Camera, Microphone, Color, etc...) and implement it.
- Write extensions. Extensions are often wrappers for any C library on a POSIX system, much like perl, python, or ruby support extensions.
- Do a translation of the manual.
- Help with writing documentation.
To help, there are several ways to get started contributing to Gnash. One is to contribute patches via the Gnash Patches site on Savanah. Once several patches have been accepted, write access can be granted after signing the FSF copyright forms required for any GNU project.
Patches can also be emailed to the firstname.lastname@example.org web email list, although using the web site is prefered. The more people working on Gnash, the sooner the free software community will has it's own Flash player technology that's functional enough to replace the proprietary one.
Due to licensing issues, it's preferable if people wishing to work on the Gnash core from the US have never signed the Adobe EULA for the commercial plugin or IDE.
Although this article  covers a specific project (Gtk+) and not everything in it is applicable to this project, it may have some material which we could borrow, as it addresses maintainability of FLOSS projects and making it easier for people to volunteer.