Besides, Mozilla is not trying to tie down anyone to it's platform, because the platform is basically the Web, which is open to everyone. There are many things which distinguish it from other platforms like you can host your "apps", which are nothing more than simple websites, on your own site and not necessarily Mozilla's MarketPlace. Mozilla is working hard to reduce the memory footprint and make the apps responsive[1] and by the time it comes out, I think it's going to have a really good performance.
I've filed a bug regarding this : https://bugzilla.mozilla.org/show_bug.cgi?id=806311 Feel free to add your system information on that bug or describe what you faced or any other constructive input possible there. You can also CC yourself to follow along the progress.
Btw I tried this in the latest Firefox nightly and it seems that the nightly doesn't crash although the CPU usage does go up to 50%, so it seems that this bug has been fixed and will be released in the upcoming stable releases.