Have you tried to disable other addons? (Click Firefox > Addons > Extensions, disable all extensions one by one but Google toolbar and restart Firefox)

Hi Danieldesira,

Thanks for the solution, it worked!!! I disabled extensions one by one except Google Toolbar. I observed that the gap was removed only after removing Norton Toolbar 5.6 version. For now, I have removed the toolbar of Norton but it seems necessary for security purpose. Can we keep it on and still hide since in the empty row it generates in Firefox is not showing a single button or anything else.

Thanks.

I don't know whether Norton supports this option. I suggest asking Norton about this. In my opinion Norton/Symantec should include an option to turn the toolbar to a minimalistic button which does not waste so much web site viewing space

Welcome ;)

May be, can ask the same to Norton. Again thanks for helping me out.