That's pretty hypocritical of Mozilla. About a year ago, they were flaunting similar ambitions[1] and actively working on Screaming monkey[2].
Quote, "Mozilla is developing a plugin for Internet Explorer that will add support for the HTML5 Canvas element. Microsoft's attempts to stifle adoption of open web standards could soon be circumvented by plugins that bring Firefox technology to Internet Explorer."
Talk of double standards...
[1] http://arstechnica.com/software/news/2008/08/mozilla-drags-i...
HN discussion: http://news.ycombinator.net/item?id=280375