After recent discussion on the GAWDS it has been found that Firefox has a problem with Flash.
Firstly find a pge with Flash on it, there are a few listed in the GAWDS sites of the month. Then try tabbing through the links. It will appear that you cannot tab past the link before the flash.
This may be fixed when version 7 of Flash is installed (untested), but as a designer you are not going to know what the visitor actually has installed. Now you may be able to set it to require version 7, but is that really necessary?
<a href="#menu" onkeydown="location.href = 'index.html#menu'">jump flash</a>
Obviously the id referenced should appear directly after the Flash on the page.
I hope this is useful for someone out there!