We offer a tarball for Linux that contains a command line installer. The problem is you just requested a dpkg. Others might want a .deb or a .ipackage or a .rpm or any other package flavor. There are fewer package management systems than there are Linux distros, but that doesn't mean there are still a lot.

Additionally, distros tend to want to manage the package building themselves. Some groups want to add in tweaks or configuration templates. Others want to include their own pages or optimizations. We can't logistically consider trying to manage all that centrally, nor would we want to take the control away from those distros.

So, I agree, you do get a slightly less comfortable distribution mechanism for the browser. You get additional control and choice depending on the distro you chose though.

What Mozilla does endeavor to do is make sure that the core code works well on all three platforms. That is where we feel it is most valuable to dedicate our resources.