This property was removed from HTML in 2010 "since UAs are removing support":
http://html5.org/r/5063
However, Blink, WebKit and IE11 still support it. Firefox does not,
nor did the last shipping version of Presto.
The usage is fluctuating between 0.05% and 0.075%, which is higher
than most removals I'm aware of:
http://www.chromestatus.com/metrics/feature/timeline/popularity/207
The profile content attribute doesn't actually do anything, but that
doesn't mean nothing could break by removing it. Still, Firefox seems
to get by without it.
The cost of supporting it is 1 line in HTMLHeadElement.idl.
What to do? Deprecate+remove or ask for it to be put back in the spec?
Philip