Computer 1: ubuntu, running Firefox 3.5.8
Computer 2: Running Windows, with cygwin, and cygwin/X.
I ssh from computer2 to computer1, run "export DISPLAY=computer2:0.0", then start firefox. First, I will get a window on computer2 that says "An error occurred while loading or saving configuration information for firefox. Some of your configuration settings may not work properly." It has a "Details" button, and an "OK" button - but does not respond to clicks of either. It also does not respond to clicking the "X" on this window. Eventually, the main Firefox window will come up, but it is extremely slow. One up, everything is extremely slow - it'll take 30 seconds from when I click the "down" arrow on the scrollbar before it even starts to scroll. If I use the -X option of ssh, there is no change.
If I am on computer1, with display set to computer1, everything works normal.
If I am on computer1, with display set to computer2, everything works normal (firefox displays on computer2, and works at normal speed).
If I am on computer1, ssh to computer2, set display to ":0.0", everything works as normal (firefox displays on computer1, and works at normal speed).
If I am on computer1, ssh to computer2, su to a different user, set display to "computer2:0.0", everything works as normal (firefox displays on compute2, and works at normal speed).