Keys sending non-US characters don't work in Firefox

[dreamlayers]

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This was examined in Windows 7 using a SDL 2 build of Em-DOSBox.

In Chrome 57.0.2987.98 (Official Build) (32-bit), when I use the Croatian keyboard layout, keys which would send non-US characters ([];') send US keyboard layout characters for those keys. This is like the official 0.74 build. However, z and y do get swapped to their Croatian layout places, unlike in the official 0.74 build

In Firefox 52.0 (32-bit), keys which send non-US characters have no effect. This is not okay. Z and y also get swapped.

Note that you can set keyboard layouts inside DOSBox, independently of the OS. To get a Croatian layout, you could use keyb yu for the Yugoslavian layout. The keys which send non-US characters have no effect in Firefox even after keyb yu. With both the Croatian layout set in Windows and keyb yu in DOSBox, the z and y are also swapped twice, back to their original US position. In Firefox, the workaround would be to use the US keyboard layout in the OS and set the keyboard layout in DOSBox if you need those characters. It would be nice to simply use the OS keyboard layout.

[dreamlayers]

Just created Emscripten issue for this: https://github.com/kripken/emscripten/issues/5022