I don't see a problem. I think it's supposed to be like that.

Can you identify that area if right click and select Inspect Element?

• https://developer.mozilla.org/en/Tools/Page_Inspector
• https://developer.mozilla.org/en/Tools/Page_Inspector/HTML_panel

right click not work on bottom white area.

Start Firefox in Safe Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.org/kb/Safe+Mode

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

See also:

• http://kb.mozillazine.org/Corrupt_localstore.rdf
• https://support.mozilla.org/kb/Toolbar+keeps+resetting

i uninstalled my Firefox completely. then installed Firefox 15 beta. the problem is still exist. but more clear. in every firefox start for a moment firefox is same pic.

if white line not removed, then if i right click on Add-on bar and click on "Customize..." then i close Customize Toolbar, white line will remove.

Did you try Safe mode or disable all extension and switch to the default theme?

• Help > Restart with Add-ons Disabled

• https://support.mozilla.org/kb/Safe+Mode

in Safe mode there is not problem.

If it does work in Firefox Safe-mode then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears.

• Use "Disable all add-ons" on the Safe Mode start window to disable all extensions.
• Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

• Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available"