Since a few days ago the navigation links for navigating beween directories on mxr.mozilla.org seem to gone. Example: When you go to http://mxr.mozilla.org/mozilla-central/source/dom/events/ there should be some text links between "Mozilla Cross-Reference mozilla-central " and "Search for: within this directory " which you could click on to go directly to "source/dom" or to "source/" (top-level source folder in this case). Not sure why these are missing, did an MXR update happen?
It's a bug introduced while fixing a different issue; waiting on new patch.
Reverted change, pending a better fix.