The new breadcrumbs in the header should make more visible that they are actually clickable. Currently only the text color changes slightly when one is hovering the mouse over the breadcrumbs. Additionally, the new popup menu is shown immediately, which is also non standard and should at least have a small delay.

I think it would be more appropriate, if the breadcrumbs use the same link styling as the side bar items, i.e., the background color changes. This is the way others (like GitHub) implement it. This was also the style we used in previous versions of Jenkins, so I consider this as a regression as well.

Now new users might do not see at all that the breadcrumbs are clickable and are distracted by the popup menu, which probably is not what they want to open.