Why can't I click on certain parts of my screen only when using firefox. I can not use the top part of my scroll bar, but can use the bottom. I cannot click on the top part of any sites, but can click on any other part of the site.

When using firefox, I cannot use my top arrow or click on the top part of the scroll bar to make it move. I can use the middle and bottom of the bar. I also cannot click on certain items that are on a certain part of a web page (top section). When I use firefox to open my email the same thing happens. I cannot click on the top part of the email page such as the delete tab, check email tab, etc. I can however click on everything when I use internet explorer, so I'm not sure if this is a firefox issue or not. Thank you