a confirmation notification pops up whenever i want to close a window

Any web site or just Facebook?

the problem is mostly with facebook.occasional with other websites

That has been reported to be caused by a Facebook extension for Firefox or by Facebook widgets.

Start Firefox in Use Troubleshoot Mode in Firefox to check if one of the add-ons is causing the problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).

• Don't make any changes on the Safe mode start window.

See:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems