My passenger side window will roll down from the drivers side, but not from the passenger side.

It sounds like that's true of everybody elses XJ as well.

I read about the paperclip fix, but I haven't really seen anything that explains what is actually wrong with the window control. Is the the actual switch, or something else?

 

Well if you do a lock bypass use wire and quick connects, NOT the paper clip, and the issue is with the window lockout button....keeps itself in constant lock mode for some reason, the thread you read about just bypasses it and works great.

If you were still worried about having a lockout, connect a toggle into the wire that connects the other two, I know theres a thread with pics on the correct way with wire too!

 

I think the wiring for the windows is too light. See the circuts for the passenger windows go through drivers panel and then back to the individual window. there is alot of voltage drop in the circut. By bypassing the lockout switch, big drop there alone, you reduce some of the drop. Another solution is to wire each passenger circut direct from the switches to their individual motors direct. Then running a seperate circut for the drive control.