I am currently running Firefox 5.0 on Arch and I cannot access the login/register links in the forum header because they are under the Arduino Forum layer.
I had to use Chrome to solve this alignment problem and enter.
I think this might be a more general problem than just mine, because I have no issues with any other site.
I figured it out:
Firefox 5.0 + Arch + Privoxy = wrong header alignment
Firefox 5.0 + Arch - Privoxy = right header display