orca/firefox: table navigation in aria grids says all cells are empty

Here is a WAI-ARIA grid

<!-- test.html -->
<title>Test</title>

<div role="grid">
  <div role="row">
    <span role="gridcell"><a href="#">First</a> table cell</span>
  </div>

  <div role="row">
    <span role="gridcell">Second table cell</span>
  </div>

</div>
<!-- end test.html -->

1. Open this file in firefox, with the Orca screen reader enabled.
2. Press t to jump to the top of the table.
3. Press alt+shift+down to move down one cell.

You hear "blank, row two column one". "blank" meaning "empty".

Expected result: Orca should read the text in the table cell; in this case, "Second table cell, row two column one".

It's probably a firefox bug, but I don't know how to find out (other than digging into the code).

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: gnome-orca 3.0.0-0ubuntu2
ProcVersionSignature: Ubuntu 2.6.38-8.42-generic 2.6.38.2
Uname: Linux 2.6.38-8-generic x86_64
Architecture: amd64
Date: Tue Jun 28 14:12:20 2011
PackageArchitecture: all
ProcEnviron:
 PATH=(custom, user)
 SHELL=/bin/bash
SourcePackage: gnome-orca
UpgradeStatus: Upgraded to natty on 2011-06-19 (8 days ago)