Mavericks.

Please make sure of the following:

• Firefox hangs or is not responding - How to fix
• Troubleshoot Firefox issues caused by malware
• Diagnose Firefox issues using Troubleshoot Mode

Please post back with the results, and we can further investigate :-)

This just happened to me, too. I suspect it was the result of Cmd-Q quitting Firefox while it was in full screen mode.

Try clicking the green plus in the upper left corner of the window. This expands the window to fill the screen but then you should be able to resize and move it again.

Hi Chris Snyder, thank you for posting. Is this happening in Firefox version 32 as well? If so if you could start a new question with troubleshooting info we can investigate further.