Like the iLiad, the XO should be able to run
FBReader. I think the XO is running Fedora under the hood, so all you might need to do (from a command window) is
Code:
su -c 'yum update fbreader'
This is from FBReader's
Desktop Download Page.
For info on yum in the XO see
Xo setup user guide. If you use su to login as root directly (as described here), then just use the command
Code:
yum update fbreader