If you had a mouse, moving the pointer up to the top of the screen would drop-down the toolbars so you could click the "3-bar" menu button and then Full Screen. Not sure if that works with a finger.

it doesn't work with fingers.

If you drag in from the left side of the screen to use the app switcher, does Firefox go back to normal? (That idea is based on having played with a Surface running RT, but I think full Windows 8.1 has something similar.)

For a fraction of second it does but then again the same full screen.

If you use the Windows button to switch to the Start screen, scroll down to all programs, and tap the Firefox icon to open a new window, that one shouldn't be full screen. Does that work?

I'm still not sure what to do about the existing window. You might have to kill it.

No, it still loads in full screen. First it loads in normal window but then after a second it goes to full screen.

This is why I use Windows 7. But I digress. Hopefully someone with more Windows 8 expertise will be able to suggest a solution. For now, you might just kill the window using the usual swipe down from the top edge to bottom edge gesture.

If you are in full screen mode then hover the mouse to the top of the screen to make the Navigation Toolbar and Tab bar appear.
Click the Maximize button (top right corner of the Navigation Toolbar) to leave full screen mode or right-click empty space on a toolbar and choose "Exit Full Screen Mode" or press the F11 key.

If i had a mouse or a way to connect a keyboard to my tablet PC, don't you think i would have already tried those options? Please. Try for a better solution.

(If you get desperate, or perhaps for future reference, the Microsoft Comfort Mouse, which connects using Bluetooth, works nicely with Surface tablets. I got someone one at our local Staples. http://www.staples.com/Microsoft-Scul.../product_187956)

Some people have had trouble with your Website Logon Plugin. As a quick check you might try disabling it.

Found your solution! had the same problem today. swipe left from the right side to bring up the charms menu (it has the settings, power, start button ect.) in the lower right you'll see six buttons, one is the virtual key board. hit this, now you have a key board!

in the lower left there will be another keyboard button on the keyboard, this lets you change the style of keyboard so you can get the F keys. you want the one with the most keys and the "FN" (function i believe) button in the lower right. hit that FN button and you'll change your number buttons to F-number buttons. hit F11 and you're there.

Sorry this is so complicated but it works. i'd post a vidieo but i don't have that capability.