Althougth in 4 of those 5 losses those fighters had a significant height and reach advantage. PBF doesnt have that over MOsley.
I think that is part of it but he must also utilize the jab to offset PBF's rhythm and viciously attack the body once he gets inside to slow him down. Headhunting Mayweather early in the fight is pointless because chances are you will be swinging at air. In the later rounds Mosley has to throw lots of combinations and pray something lands on a tired Mayweather. However, I do not know if Mosley can sustain a high workrate anymore at his current age especially without the use of PEDs and the like which would be impossible because of the random drug testing implemented by both parties. Shane has trouble with good boxers but not against sluggers. He'll be at least a 3:1 underdog in my books against Mayweather.
mosley had been outboxed before and lossed against cotto, forrest and wright. he was dominated in his first matches against forrest and wright. now mayweather is a better defensive fighter and a more accurate puncher then those guys but mayweather is also smaller then those guys. mosely can afford to be more physical with mayweather and have sucess then he did against cotto, forrest and wright. mosley has to keep mayweather on the ropes and and keep the fight at close quarters. and keep and balance attack, head and body. also captalize on the fact that mayweather is not a volume puncher. he has to get off first. mosley also has the power to hurt mayweather. he needs essentialy repeat what castillo did to mayweather. and mosley can even be more effective then castillo because he is alot faster then castillo he does this, he can win a decision but all this is easier said then done.
I see 3 things that they can do: 1. JAB! 2. Lean on Mayweather constantly, whenever there is a clinch (and there will be alot of them), Mosley needs to lean and push mayweather and hopefully tire him out. Mosley is much stronger, much stronger then anyone mayweather's faced but that won't matter if he can't hit him, so he has to impose his strength in the clinches 3. Try a Jab-Left Hook Combo That's it. Shane's lead looping right hand will be completely neutralized in this fight