The stumbleupon extension was removed from the archives a few days ago [0]. The app-install-data-ubuntu package has not been updated since then, which is why it is still being displayed in software-center.
[0] https://launchpad.net/ubuntu/lucid/+source/stumbleupon/3.3.8-3build1
The stumbleupon extension was removed from the archives a few days ago [0]. The app-install- data-ubuntu package has not been updated since then, which is why it is still being displayed in software-center.
[0] https:/ /launchpad. net/ubuntu/ lucid/+ source/ stumbleupon/ 3.3.8-3build1