Microphone input level normalization

I have a problem using the JavaScript Web Audio API from the moment Firefox was activated until version 31. The source of my script has not changed.

What is he doing? I am using mic input (generated signals placed through 3.5mm jack in PC) -> amplification -> rendering with ScriptProcessor node. And - everything worked fine, but now it seems to me that the input levels are somehow normalized before going to the GainNode. As a result, the waveform visualization is completely unusable. See example below:

http://i.stack.imgur.com/hzEOR.png

I cannot find a way to disable this feature. The only thing that works is to downgrade FF to version 30. I searched in the FF 31 release notes, though I couldn't find anything that could explain this behavior ...

Is there a way to solve this? Why is this happening? Thank.