Handling of landmark roles on native markup

I recently discovered that Firefox and WebKit-based browsers handle
landmarks differently.

WebKit implements the current ARIA implementation guide at
http://www.w3.org/TR/wai-aria-implementation/#mapping_role --
"For the standard role mechanism of the accessibility API, the user agent *
MUST* use the first token in the sequence of tokens in the role
attribute<http://www.w3.org/TR/wai-aria-implementation/#def_attribute>
 value <http://www.w3.org/TR/wai-aria-implementation/#def_value> which
matches, on comparison, the name of any non-abstract WAI-ARIA role."

Firefox/Gecko implements an older version of the implementation guide at
http://www.w3.org/TR/2009/WD-wai-aria-implementation-20090224/#mapping_role
"The first role token with a known mapping to accessibility APIs SHOULD be
used when mapping to the accessibility API via the standard role mechanism
of the accessibility API. Use the role table below and apply any special
case rules that are specified."

As I see it, there are two advantages to the older system:
1. The landmark role can complement native semantics without clobbering
them, e.g.
 <input type="text" role="search">
 <table role="complementary">
 <ul role="navigation">
2. It enables forward compatibility of ARIA-enabled content with future
browsers and platforms, as fallback roles can be used. For example, <table
role="calendar grid"> allows newer platforms who understand a "calendar"
role to map directly to that, but previous versions which did not know
about "calendar", would fall back on "grid", still a valid, usable role.

I'd like to help sync the browser implementations on this issue. My
(opinion) is that the older role processing is better for the reasons given
above. I would love to hear other opinions.

Thanks as always,
Aaron