For Mac OS users, there is a system setting that may not allow you to tab onto several types of elements in a web page. To change this setting:
If you don't mind using keyboard commands, you can access this directly by pressing the option key, the command key, and the p key all at the same time.
There is an onscreen way as well, simply click the text in the lower left of the screen labeled "print using the system dialog":
Note: In newer versions of Google Chrome, it's moved from the left side over to the right side of the screen. And they did something else, first you have to click on the down arrow (⋁) past on More Settings:
Then do not use the blue print button, please use "Print using system dialog ..(⌥⌘P)"
Where you used the keyboard shortcut or the clicked "print using the system dialog", you print screen should appear.
There is a possibility that the dialog will show up collapsed. To expand it, click on the Show Details button:
Then you'll see the expanded print dialog box:
With this box, you are ready to make any changes you'd like (such as number of copies, etc.) and press the print button when you are ready to print.