Websites does not show up after installation

[FormFollowsFunction]

Hi, my sister installed Filezilla today and after that no site in her browser does load any more. There is no error message. After refreshing the browser she only sees a blank page, no matter which site she is trying to load.

She told me that she can load the websites when she is connected with the router of a friend. But when she is connected with her own router, it does not work

I googled for that problem and searched the forum, but found no similar topic.

I would appreciate your help very much.