Comment 471 for bug 412647

There are several reasons why we decided to build the SDK against the system CRT msvcrt.dll, but the most important one is that if you decide to link against any of the VS ones you will be forced to distribute broken software.

According to MS EULA you can't distribute yourself this "system library" (eg: msvcr100.dll) so your software is depending on a third party installer (Microsoft Visual C++ 20XX Redistributable Package). The GPL also forbids explicitely the redistribution of System Libraries (http://www.gnu.org/licenses/gpl-faq.en.html#WindowsRuntimeAndGPL).

How is this handled in Firefox?

There is the option of rebuilding the SDK linking against msvcr100.dll, this would require on our side providing a gcc spec that links against moldnames100 and msvcr100 and rebuilding gcc so that libgcc_s_sjlj-1.dll and libstdc++6.dll are linked against the new CRT and using the gcc spec in the toolchain.