Hi,
Support for these dongles is not the best on linux for arm devices like the Pi.
The latest Raspberry 2/3 image has a driver for the MT7601U dongle, but no firmware.
To get it working you have to download the file mt7601u.bin:
wget https://github.com/porjo/mt7601/raw/master/src/mcu/bin/MT7601.bin -O /lib/firmware/mt7601u.bin
Frank