J’ai vérifié que lsusb me donne bien les identifiants attendus :
$ lsusb
Bus 002 Device 027: ID 148f:7601 Ralink Technology, Corp. MT7601U Wireless Adapter
J’ai également installé le paquet firmware-misc-nonfree (en ayant pris soin auparavant d’activer les dépôts non-free, sans quoi j’avais une erreur comme quoi le paquet était introuvable).
Ensuite, en connectant le dongle wifi, j’ai une erreur dans les logs de dmesg :
[ 1121.788028] usb 2-2: new high-speed USB device number 93 using
ehci-pci
[ 1121.947043] usb 2-2: New USB device found, idVendor=148f,
idProduct=7601
[ 1121.947047] usb 2-2: New USB device strings: Mfr=1, Product=2,
SerialNumber=3
[ 1121.947049] usb 2-2: Product: 802.11 n WLAN
[ 1121.947051] usb 2-2: Manufacturer: MediaTek
[ 1121.947053] usb 2-2: SerialNumber: 1.0
[ 1122.076015] usb 2-2: reset high-speed USB device number 93 using
ehci-pci
[ 1122.226775] mt7601u 2-2:1.0: ASIC revision: 76010001 MAC revision:
76010500
[ 1122.228286] mt7601u 2-2:1.0: firmware: failed to load mt7601u.bin
(-2)
[ 1122.228291] mt7601u 2-2:1.0: Direct firmware load for mt7601u.bin
failed with error -2
[ 1122.228928] mt7601u: probe of 2-2:1.0 failed with error -2
[ 1156.860858] usb 2-2: USB disconnect, device number 93
[ 1160.884021] usb 2-2: new high-speed USB device number 94 using
ehci-pci
[ 1161.043016] usb 2-2: New USB device found, idVendor=148f,
idProduct=7601
[ 1161.043019] usb 2-2: New USB device strings: Mfr=1, Product=2,
SerialNumber=3
[ 1161.043022] usb 2-2: Product: 802.11 n WLAN
[ 1161.043024] usb 2-2: Manufacturer: MediaTek
[ 1161.043026] usb 2-2: SerialNumber: 1.0
[ 1161.168027] usb 2-2: reset high-speed USB device number 94 using
ehci-pci
[ 1161.318751] mt7601u 2-2:1.0: ASIC revision: 76010001 MAC revision:
76010500
[ 1161.320227] mt7601u 2-2:1.0: firmware: direct-loading firmware
mt7601u.bin
[ 1161.320233] mt7601u 2-2:1.0: Firmware Version: 0.1.00 Build: 7640
Build time: 201302052146____
[ 1161.718362] mt7601u 2-2:1.0: EEPROM ver:0c fae:00
[ 1161.903112] mt7601u 2-2:1.0: Error: RX urb failed:-71
[ 1161.903147] mt7601u 2-2:1.0: Error: MCU resp urb failed:-71
[ 1161.903151] mt7601u 2-2:1.0: Error: MCU resp evt:0 seq:5-4!
[ 1161.907359] mt7601u 2-2:1.0: Error: RX urb failed:-71
[ 1161.907613] mt7601u 2-2:1.0: Error: MCU resp urb failed:-71
[ 1161.907616] mt7601u 2-2:1.0: Error: MCU resp evt:0 seq:5-4!
[ 1161.911608] mt7601u 2-2:1.0: Error: RX urb failed:-71
[ 1161.911862] mt7601u 2-2:1.0: Error: MCU resp urb failed:-71
[ 1161.911865] mt7601u 2-2:1.0: Error: MCU resp evt:0 seq:5-4!
[ 1161.915857] mt7601u 2-2:1.0: Error: RX urb failed:-71
[ 1161.916102] mt7601u 2-2:1.0: Error: MCU resp urb failed:-71
[ 1161.916106] mt7601u 2-2:1.0: Error: MCU resp evt:0 seq:5-4!
[ 1161.920108] mt7601u 2-2:1.0: Error: RX urb failed:-71
[ 1161.920350] mt7601u 2-2:1.0: Error: MCU resp urb failed:-71
[ 1161.920354] mt7601u 2-2:1.0: Error: MCU resp evt:0 seq:5-4!
[ 1161.920361] mt7601u 2-2:1.0: Error: mt7601u_mcu_wait_resp timed out
[ 1162.116019] mt7601u 2-2:1.0: Vendor request req:07 off:0080
failed:-71
[ 1162.276012] mt7601u 2-2:1.0: Vendor request req:02 off:0080
failed:-71
[ 1162.436012] mt7601u 2-2:1.0: Vendor request req:02 off:0080
failed:-71
[ 1162.436055] mt7601u: probe of 2-2:1.0 failed with error -110
[ 1162.436288] usb 2-2: USB disconnect, device number 94
[ 1162.700024] usb 2-2: new high-speed USB device number 95 using
ehci-pci
[ 1162.859062] usb 2-2: New USB device found, idVendor=148f,
idProduct=7601
[ 1162.859065] usb 2-2: New USB device strings: Mfr=1, Product=2,
SerialNumber=3
[ 1162.859067] usb 2-2: Product: 802.11 n WLAN
[ 1162.859069] usb 2-2: Manufacturer: MediaTek
[ 1162.859071] usb 2-2: SerialNumber: 1.0
[ 1162.984014] usb 2-2: reset high-speed USB device number 95 using
ehci-pci
[ 1163.134798] mt7601u 2-2:1.0: ASIC revision: 76010001 MAC revision:
76010500
[ 1163.136216] mt7601u 2-2:1.0: firmware: direct-loading firmware
mt7601u.bin
[ 1163.136221] mt7601u 2-2:1.0: Firmware Version: 0.1.00 Build: 7640
Build time: 201302052146____
Et je lis sur ce dépôt GitHub mt7601usta que :
Note: Kernel 4.2 has been released which contains a driver for mt7601u, this repository is now deprecated.
Or je fais mes tests sur une debian stretch dont le noyau est 4.9, soit ultérieur au 4.2 :
$ uname -a
Linux nice-laptop 4.9.0-8-amd64 #1 SMP Debian 4.9.110-3+deb9u6
(2018-10-08) x86_64 GNU/Linux
Si j’en crois le dépôt en question, je ne devrais pas avoir à installer de driver complémentaire.
Et même en installant des drivers complémentaires, ça ne fonctionne pas… 
Le plus étonnant dans cette histoire, c’est le packaging blister/carton qui m’indique que le chipset est un 8188… bien loin du mt7601.