O.k. the problem with blurred fonts in the Gnome-terminal seems to be bug #190848 - so this is a different issue.
Reading through the Ubuntu-forums I got a hint, that the blurred images in Firefox may have something to do with zooming.
So if Firefox preserves the zooming-level that has been used in the last session this might lead to the impression that there is
a rendering problem. I am gonna check this evening.
O.k. the problem with blurred fonts in the Gnome-terminal seems to be bug #190848 - so this is a different issue.
Reading through the Ubuntu-forums I got a hint, that the blurred images in Firefox may have something to do with zooming.
So if Firefox preserves the zooming-level that has been used in the last session this might lead to the impression that there is
a rendering problem. I am gonna check this evening.