Top Browser Domain is empty if url is a file

[nicolae-stroncea]

I was reading a pdf on firefox, and firefox showed it in top browser domains. However, because there's no real domain, it's just an activity with a colour and a time.

I think for a case like this, the activity should either be ignored from the "top browser domains" category, or get a custom browser domain name which lets the user know it's a file.

EDIT: Another issue is that all events without a clear domain name, will get clumped together, as they all have empty strings.It's why a custom browser domain name must be identifiable from all others, i.e if i'm reading two different pdf documents on firefox, both need to look different.