What is your early experience with them?.
Here is my experience with Firefox OS:
Since source code & developement of Firefox OS is open, with help from other developers (#gaia, #b2g on irc.mozilla.org and #arm-netbook" on irc.freenode.net) recently i have ported Firefox OS to 7 inch tablet based on allwinner a10 SOC (Video - http://softonaut.blogspot.in/2012/09/tablet-running-firefox-mobile-os.html). Having worked with web technologies, enjoyed creating applications for Firefox OS (Backbone.js Todo app - http://www.github.com/selvan/gaia-spikes). You may have a look at out-of-the-box firefox OS applications at https://github.com/mozilla-b2g/gaia/tree/master/apps to explore more.