Disabling FireTray addon solved this issue. It was a little bit different for me: only the Firefox icon become blurred after opening Thunderbird.
But I think I'll keep this addon enabled since it doesn't affect usability and features of these Mozilla products.
It should be forwarded to FireTray developers to be fixed.
Thanks again :)
Thanks ockels!
Disabling FireTray addon solved this issue. It was a little bit different for me: only the Firefox icon become blurred after opening Thunderbird.
But I think I'll keep this addon enabled since it doesn't affect usability and features of these Mozilla products.
It should be forwarded to FireTray developers to be fixed.
Thanks again :)