Firefox update mania :) It seems that the wonderful idea of using update.mozilla.org to validate extensions has met with a small problem. Bandwidth. The site has fallen over, it gets up, gets hit on the head again by the hordes of people rushing to update their extensions and falls over again. rinse, repeat.
If anyone needs a mirror, I found this link in the Firefox forums. It's slow too, but at least it will split the load a bit.
