Look, I'm not going to tell that Front Squatting is comfortable. I'm not going to tell you that putting a bar on your shoulders and trying to drive it over your head is easy. But I will tell you that there are some things we can do to make the Front Rack position for both of these movements a little more effective.
The Front Rack position (the way a bar rests across the front of the shoulders during a Front Squat, Clean, or Jerk) can be really uncomfortable or sometimes even painful for some individuals. Largely, the individuals I see that struggle through the Front Rack have a hard time finding the correct positioning for the movement. This is partly because it requires that we get into Shoulder Flexion and Humeral External Rotation, and requires some mobility through Thoracic Extension.
Admittedly, my favorite drill is something that was introduced to me by Physical Therapist Quinn Henoch:
That's right, the best mobility drill for the Front Rack is to get into the position itself and progressively seek new ranges of motion.
There's a few others that I also like for getting into the Front Rack Position as well. The first is the Elbow Supported Band External Rotations, which allows us to isolate Humeral External Rotation and stabilize the shoulder. This would be considered an active mobility drill for that specific movement.
I also like to emphasize movement in Thoracic Extension to help promote an upright torso. For this I like to utilize the Kettlebell Halo In a Squat, which combines Thoracic Extension and Shoulder flexion, to open up the Thoracic Spine and reinforce positioning.
Ultimately, like Henoch says, the best way to improve the Front Rack will be to do the Front Rack. As a preparatory method, however, utilizing the other two movements prior to Front Squatting or in between warmup sets can be very beneficial as mobility tool.