Well after many year of following the Gnash development, I can successfully say that by me getting fed up with Adobe Flash Player, I've migrated to Gnash Plugin for my Firefox and Chromium browsers on Ubuntu. And Gnash has finally come to a point where it's a suitable replacement for the aforementioned.
So well done to the whole Gnash Development Team and Community. Nice effort! I'm a happy IcedTea+Gnash Plugin user. ;-)