This is needed because DOMParser is invoked on some fixture HTML that contains an
<svg> element (Walmart/Payment.html). When this happens **and** there is
a declaration for `color: MenuText` in a UA stylesheet (which is added in the next
changeset), there is a graphics crash. This is fixed in the new headless mode,
so this changeset forces the directory to run in it.
MozReview-Commit-ID: 9T8eFOW4xoz
--HG--
extra : rebase_source : d0cd013c2d1a980406c96a3fd6243ff9d2f33ed3