First of all, I have been using Mozilla software for a relatively long time. I used Phoenix, Firebird, then Firefox. I also used Mozilla suite and Thunderbird. You can safely say I am familiar with what Mozilla can accomplish. There have been memorable moments too such as the "we are finally releasing Firefox 1.0" thing.
Mozilla's attitude towards users and their feed back was always exemplary. I can tell when someone submits a crash report and Mozilla developers almost instantly figure out what is wrong that those are skilled developers.
I used to compile my own Firefox build or use unofficial ones back in the Windows XP days. I switched completely to Linux in 2004 and have been using my own builds since then.
I have also read about Firefox OS which I wish you all the luck with.
I have some wishes too. I would like to see a complete desktop environment for Linux from Mozilla. There are a lot of desktop environments for Linux. Why a new desktop environment?
The simple answer is because Mozilla can do it and it can be based on existing Mozilla technologies or future ones. It also is a new market to enter and it may be something that the Linux desktop universe needs.
Thank you for reading my wall of text :)