Do you have any Microsoft application to be opened on your homepage  ?. I
mean, there's a chance that you have a web part which displays one of the
microsoft's application on your homepage and for that the SPS doesn't has
the profile info or whatever, for it to display and hence it wanted to
install something for it to open  up the application(s). Like I have the
public folders, calendar etc. on my homepage. For example, outlook, notes
etc. But that could be the Ms Digital Dashboard too....but that normally
asks for permission to install. So just check it up...