Problenm is not the gray bar, but bottom 1/3 of screen.
Problem with bottom 1/3 of screen, and not with gray bar.
Alla svar (2)
Please provide a screen shot. https://support.mozilla.com/en-US/kb/Adding+screenshots
http://www.wikihow.com/Take-a-Screenshot-in-Microsoft-Windo...
Can you attach a screenshot?
Use a compressed image type like PNG or JPG to save the screenshot and make sure that you do not exceed the maximum file size (200 KB) and do not click Preview after you have attached the image. --- Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes). See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems
If it does work in Safe-mode then disable all your extensions and then try to find which is causing it by enabling one at a time until the problem reappears. You can use "Disable all add-ons" on the Safe mode start window. You have to close and restart Firefox after each change via "File > Exit" (on Mac: "Firefox > Quit")