kripken/emscripten — pull request #839 by tobiasweibel (2013-02-08 10:50:39+00:00)
Title: Implement Firefox workaround for "TypeError: anonymous method called on incompatible string"

My theory: It seems that Firefox optimizes sometimes too hard and therefore 'value' in 'ccallFunc/toC' is some kind of unassigned. Then calling 'value.length' in the 'toC' method throws an exception. With the concat of an empty string we can workaround that problem.