[Bug-gnuzilla] Wrong Information about OS!

[D.P.Pandya]

I am using Trisquel 7.0 GNU/Linux (http://trisquel.info/).
Abrowser (https://trisquel.info/en/wiki/abrowser-help) is pre-installed. 
Information about browser is provided by "navigator.userAgent"

The out put of "navigator.userAgent" by Abrowser is:
Mozilla/5.0 (X11; Linux i686; rv:33.0) Gecko/20100101 Firefox/33.0

-> I installed GNU IceCat 31.2.0 on my syetem by `sudo apt-get install 
icecat`.

-> And The out put of "navigator.userAgent" by GNU IceCat is:
Mozilla/5.0 (Windows NT 6.1; rv:31.0) Gecko/20100101 Firefox/31.0

Here you can see that IceCat shows "Windows NT 6.1"!. So, Why IceCat is 
giving wrong information about OS?
How do I fix this?

___________________________________________________________________________________
The problem is websites getting wrong information about my OS. example: 
Gmail account activity information, etc.