If you are running Firefox, try "Restart with Add-Ons Disabled..." and try the various web sites, if they work, you'll know for certain that it's one (or more) of the Add-ons. Restart FF in normal mode and begin disabling add-ons until you find which one is causing the problem.
Since you are experiencing the same issue with other sites, this is clearly not a problem with duckduckgo.com, so you will find it more productive to get support from Mozilla (again, assuming that you are using FF).

x-15a2Forum Moderator