How do you debug printable CSS?

Question

I use Firebug and IE Developer Toolbar all the time to debug tricky CSS problems. But occasionally, a tricky bug comes up that only appears when you go to print the page.

Answer 1

Just found a comment by lee-penkman about a new feature in Firefox here: Press Shift-F2 in Firefox to open the browser console (not the javascript console), then enter media emulate print. Works absolutely great!

---

Update Sept. 2018: Starting with Firefox 62, the developer console has disappeared. There doesn't seem to be a way to activate print style emulation now.

---

Update Nov. 2019: It seems that in Firefox 69, there is again a new button for print style emulation. See the other answer on this page: https://stackoverflow.com/a/58015662/195476