Why do advertisements appear at the top or body of the website that was provided by the site visited?

No, '''Firefox''' doesn't add garbage like that. More than likely you picked up a dose of Malware. Install, update, and run these programs in this order. They are listed in order of efficacy.<br />'''''(Not all programs detect the same Malware, so you may need to run them all to solve your problem.)''''' <br />These programs are all free for personal use, but some have limited functionality in the "free mode" - but those are features you really don't need to find and remove the problem that you have.<br /> ''Note: If your Malware infection is bad enough and you are mis-directed to URL's other than what is posted, you may have to use a different PC to download these programs and use a USB stick to transfer them to the afflicted PC.'' Malwarebytes' Anti-Malware - [http://www.malwarebytes.org/mbam.php] <br /> SuperAntispyware - [http://www.superantispyware.com/] <br /> AdAware - [http://www.lavasoftusa.com/software/adaware/] <br /> Spybot Search & Destroy - [http://www.safer-networking.org/en/index.html] <br /> Windows Defender: Home Page - [http://windows.microsoft.com/en-US/windows7/products/features/windows-defender]<br /> Also, if you have a search engine re-direct problem, see this:<br /> http://deletemalware.blogspot.com/2010/02/remove-google-redirect-virus.html If these don't find it or can't clear it, post in one of these forums for specialized malware removal help: <br /> [http://www.spywarewarrior.com/index.php] <br /> [http://www.spywareinfoforum.com/] <br /> [http://bleepingcomputer.com]

Can you attach a screenshot? *http://en.wikipedia.org/wiki/Screenshot *https://support.mozilla.org/kb/how-do-i-create-screenshot-my-problem Use a compressed image type like PNG or JPG to save the screenshot.