These are all good suggestions. You shouldn't have to stop the set due to shoulder pain before your legs tire, so try out some of these things, but a little pain is normal, and bruised delts are normal too.
I had pain for a while,but it went away in time.If its getting to you alot and you feel like the pain isnt going to go away,you might look into buying one of those sting ray things(I think thats what they are called..by the same people that make the manta ray for back squats,only these are for front squats.They feel good)
ye i remember when i was doing front squats my shoulders would get all bruised and torn up, i just sucked it up and put it in the back of my head and forgot about it, but i like a little pain =)