UNIX pipes

why does this work: firefox yotsuba.jpg
but not this: ls|grep yotsuba|firefox

note: ls|grep yotsuba produces: yotsuba.jpg

what am I doing wrong?

>>25
You are a dumbfuck.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
  <topic>
  <title>Dis XML yo</title>
    <var>
      value
    <var>
    <anothervar>
      value
    </anothervar
  </topic>
</xml>

This is a valid XML file. Now please tell me why it can't be edited with a text editor.