One option is to use the built in browser - http://www.mobileread.com/forums/showthread.php?p=1726641
The other is to install a dedicated VNC program...
Be sure to remove the USB cable when it says to, otherwise it won't work.
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Install KUAL (Kindle Application Launcher) - http://www.mobileread.com/forums/showthread.php?t=203326
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Install USBNetwork hack - http://www.mobileread.com/forums/showthread.php?t=88004
You have to fiddle around with the config a little bit here. I couldn't get networking going over USB between a Mac and the Kindle so I enabled WiFi and that seemed to work.
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Install the KindleVNCViewer - download the zip from this thread http://www.mobileread.com/forums/showthread.php?t=150434
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Setup a passwordless VNC server on the Mac. I used RealVNC server and disabled the keyboard and mouse controls.
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SSH into the Kindle and run
cd /mnt/us/kindlevncviewer/kindlevncviewer
./kvncviewer YOUR_IP