This is an old post, but I found that in firefox the axis don't take values from -100 to +100, instead they take values from 0 to +200. So to make your game playable for both chrome and firefox just add a global variable (ex. AnalogDebugNumber) and use it in your axis comparison like this:
if the player is using Chrome, set AnalogDebugNumber=0,
and if the player is using Firefox, set AnalogDebugNumber=100
I hope this helps someone.
I don't know if there is an automatic way to check the browser the player is using but you can always let the player pick their browser in the game options and set the AnalogDebugNumber accordingly.