Gijs suggested that we add tags to the mochitest that we have for the urlbar, at least whilst we have them referenced across two directories.
This means we can do things like:
$ ./mach mochitest --tag quantumbar browser/components/urlbar/
$ ./mach mochitest --tag quantumbar browser/components/urlbar/tests/browser/browser_urlbarEnter.js
and only the quantumbar related tests will run.
(you can do just
./mach mochitest --tag quantumbar but that takes longer as it has to check all the test directories).
I'm also tagging the legacy tests as 'urlbar' so we can run just those as well.