I intend to upgrade my FireFox Sniper V to electric, by replacing the front wheel with a motorised kit wheel. My question is that the wheels (both) are quick-release: is it safe to motorise this bike.
! - the motorised kit wheel is bolt on type.
Yes, probably and maybe. I'm unfamiliar with your bike model, but I have run my own ebike front motor for a couple years.
To answer your question - the old wheel is quick release, but the replacement one will likely be a bolt-on wheel. It is possible to use quick release adapters, but wheel nuts are more secure and will hold the anti-spin washers better than a QR.
The main problems stem from design of the front forks and power of the motor. As your motor powers on, the torque is transmitted through the axle. Over time the dropouts get chewed out.
What is the wattage of your motor? Anything under 300 watts doesn't have enough impulse power to cause a problem. If you have over 500 Watts then a torque arm will help keep your forks working.
Do you have disk brakes? Your motor kit has to have bolt holes to support the rotor in the right place. This is not an issue for rim brakes, but your rim brakes need to be working perfectly to cope with the extra speed and momentum.
Yes, it is safe, because motorized wheel will be firmly attached by the bolt mount.
Have you perhaps looked into going with a rear wheel motor or even better a central drive, (Bafang-8Fun- has great affordable models now at different power levels.) that will allow you to really leverage the bikes gearbox with the motor to make it a "Real" hybrid Bike-electric... As it is the speed increase to 20+ mph means you should perhaps look into Hydraulic or mechanical disk brakes with decent rotors, Stopping is EVERYTHING on an Ebike and if you are in city stop -go traffic I think they're better. The law allows upto a 750watt motor (Federally)but a 36v (or 48v) 500w mid drive, I think would be the better solution and perfect power level to still allow you to retain the 'Bike feel.'
Lucky you ;) As for myself, living in New York, USA (Brooklyn,) I know that by United States Federal Law All Ebikes under 750 watts are legal WITHOUT a License, Insurance etc BUT In New York City ALONE, they are currently illegal by city code, to rid on public streets, (Though a Law to revise that, is currently doing the rounds in the NY State legislature.) It's also legal I believe in NY Parks on paths (e.g NYC's Prospect or Central Parks (It's not so easy to find a current definitive standard Ebike guide to post @the moment that is correct for EVERYWHERE in the world, BUT if I find one I will again update this answer to include it) and obviously private 'off road' areas are good too... Rear wheel quick releases axles are not as sturdy as a through axle but for a 500watt or 300w motor, like yours, it should be fine and likely won't need a torque arm either, unlike a front wheel hubmotor setup, in which case I'd advise installation of the Torque arm to support the stress on your forks... About the disk brakes, I Hope you will consider getting brakes with electric motor cutoff switches, they are not that expensive (For Mechanical @least) and when paired with decent rotors 160mm or better 180mm, will really enhance your braking, as your not fighting the motor too and are therefore a quite vital safety feature for an Ebike in my opinion.