Steven,
After I saw your post, I tried this and found the same behavior with Firefox version 3 and Tools Release 8.97.0.2. It appears to try and open pages, but only the form heading is displayed. No grid is displayed.
For what it's worth, I looked on Oracle's Customer Connection site and found that Firefox version 3 support is planned for future (beyond 8.97) tools releases, but not yet supported.