hi, please try to clear the cache & cookies from yahoo.com and reload the page.

Hi Philipp, I've cleared the cache & cookies but I still can't attach anything to an e-mail.

You can check if your plugins are up-to-date.

• https://www.mozilla.org/plugincheck/

Your System Detail list shows an older Shockwave Flash 11.8 r800 version. You can find the latest Flash player versions for Firefox on this page:

• http://www.adobe.com/special/products/flashplayer/fp_distribution3.html

It is possible that security (Anti-Virus, firewall) is causing problems. Try to disable security software temporarily to see if that makes a difference.