AddThis

Can´t view website as AddThis banner won´t close

On 100´s of websites I visit the page will open as usual for a few seconds and then automatically skip to the AddThis programme where you have a list of social media you can share / bookmark.
This takes up the WHOLE SCREEN and I cannot view ANY of the original website, plus it doesn´t close, nor can I uninstall it. If i reload the page exactly the same will happen so I can´t currently view any website that uses AddThis (that seems to be the case anyway).

Any ideas? I´ve restarted, cleared all my cache, installed addthis, uninstalled it, changed screen resolution and updated firefox but still no luck.