Gnash is a Free Flash movie player, which works either standalone, or
as a Firefox/Mozilla plugin.

Gnash supports the current Shockwave format, version 7. While all the
ActionScript classes exist, not all of the methods defined by the SWF
format documentation are implemented however, so not all flash movies
work 100% if they utilize any of the unimplemented methods. This is one
of the areas to work on to achieve full version 7 compliance.