If you need to print a web page automatically with Javascript and you don't want the user to see a print dialog box, you can do that with Mozilla Firefox if you change a user's setting in Firefox:
A user can set a preference to print without dialog box.
Go to about:config (Type this in the address bar)
Right click on any preference and select "NEW" > "BOOLEAN" IMPORTANT: DO NOT SELECT STRING or NUMERIC as this will not work if you are an idiot (like me) and select "STRING"
type: print.always_print_silent
Hit OK
type: true
Restart the browser. This writes a line to the prefs.js file (on windows) (or the user.js file on Linux?) the next time you start the browser, any javascript print(); command will print directly to the printer using the currently configured print settings. The exact syntax is:
<a href="#" OnClick="window.print();">PRINT THIS WINDOW</a>
NOTE: THIS DOES NOT AFFECT WHAT HAPPENS WHEN A USER JUST HITS THE PRINT BUTTON. ONLY WHEN YOUR HTML CODE CALLS THE JAVACRIPT PRINT COMMAND.