The USB stick has recently been crashing Explorer as I write a file, it is really slow, and trying to copy the browser over this time resulted in "Failed to copy firefox.exe: Path is too deep".
I got this on my flash pen aswell, except I was copying OpenOffice. In my case, running scandisk on the USB filesystem fixed the problem.You need to remember that removable strage devices for the most part, are still using FAT-32 which isn't exactly the most robust filesystem in the world.