Good news that one XT suhu named Adhyt Aza from Indonesian XTers community to find a way without damaging that usb tethering function!
he was test several times in FIRE XT530 & some chinese android phone and the result is 100 % work
Here we go!
* SnapPea for its drivers http://www.snappea.com/windows
* Vroot to its root https://www.dropbox.com/s/2qj2stvyst...3882_Setup.exe
1. Please install its snapPea - in pc , then enable USB debugging ( application> develoment > usb debugging ) and connect it to the pc
2. So SnapPea applications will respond and detect our Phone , if not detected please install drivers manually from phone & open again snapPea
3. Install the application VROOT on pc , let VROOT detect Our Phone type , when it is detected please click the green ROOT
4. Wait about 2 minutes and VROOT will execute our FIRE XT
5. Then Our XT will restart itself when VROOT already finished executing , when it entered the home screen, please close VROOT and disconnect the usb cable
6. Voila! Please check your Application drawer and if you see this then your xt is fully rooted without break Usb Tether!
NB : used windows 7 32 bit