This offen happen, when you install Yahoo toolbar addon to firefox 3.5 version.
The solution to this issue is
1.Goto Tools option of firefox
2.click on Add-ons
3.Click on the extension section
4.You will find Yahoo toolbar, Disable it or uninstall it.
5.Then restart your firefox.
You will find your mouse right click working fine,
Enjoy saving image and opening lots of tabs using mouse right click in browser.
This will solve your Mouse Right Click Not working in firefox issue.
Hope this post will help you,
if yes please put comment below of this page,
Indianic Infotech Ltd (India)
Monday, January 25, 2010