I can be wrong but it may be a permissions problem (Ubuntu has a lot of them
and I only started to notice this after trying to install a Thermal Printer
in it).
Try this (it is temporary so don't worry):
1 - Find where the printer is located in the /dev/ directory but it should be
something like /dev/usb/lp0 and do the fallowing command on the terminal :
sudo chmod 777 /dev/usb/lp0
2 - Start the printer configuration to see if it found the printer like this:
sudo system-config-printer
If it shows the printer on the list (when it's not already manually installed
on cups) then it is a permissions problem that can be solved with a "rule"
(and should be added to the final version of Trisquel 6.0.
Otherwise it is a missing driver (it may happen, the driver can be missing,
or worse, can be proprietary). If it's the case then install this (licensed
under GPLv2, BSD and MIT licenses) -->
http://hplipopensource.com/hplip-web/models/deskjet_aio/deskjet_2510_series.html
And everything should work like a charm.
