Doxygen breadcrumbs poorly formatted in web browsers

[Sqeaky]

When generating doxygen docs the docs work but are poorly formatted. The header produced show the list of bread crumbs in a single vertical line instead of several horizontal rows, see attached screenshot:

Here are the steps required to duplicate, starting from the directory with this repo checked out. These were done on an ubuntu 17.10 machine with firefox 57, chromium 63, cmake 3.9.1 and doxygen 1.8.13:

$ cd ../
$ mkdir Mezz_StaticFoundation-build
$ cd Mezz_StaticFoundation-build/
$ cmake ../Mezz_StaticFoundation -GNinja
$ ninja
$ ./StaticFoundation_Tester  # Not required but it is worth noting that all tests passed
$ chromium-browser Doxygen/html/index.html 
$ firefox Doxygen/html/index.html