It took a while to start working on Bug 563317 (Install Visual C++ 2010 on build slaves) and get it working properly.
The second challenge was awaiting me after I deployed the package on the try build slaves. Our start-buildbot.bati batch file was setting Visual Studio 2005 environment variables and it was not easy to reset those variables easily. After a bunch of try pushes the solution was pushed!
So, if you want to compile Firefox with Visual Studio 2010 using try server, add the following line to the end of your mozconfig:
P.S. To have talos tests for debug builds running properly we still need to fix Bug 701700 and deploy VC++ 2010 debug CRT on talos slaves.