Linksys with mac pro & firewall issue when printing

I print from a Mac Pro Laptop which uses the Lion OS...the latest version. I have a Canon Printer MX870series. Cox Cable set up our network with a Linksys by Cisco Router a couple of years ago. Now when I attempt to print, I get a communication error. I called Canon and they helped me download an update on the printer driver. I was instructed to make sure my Firewall in the System's Preferences (Security) was turned on...it was. I was able to print. Then I began getting the error message...so I turned off the Firewall and was able to print.