Brief No-Theme Period

My test site is http://www.tikuiaku.com/drupal

I'm noticing that (nearly) every time I click a page, there's a half second to a second when all of the content is loaded, but the theme isn't at all (white background, black text, default Times New Roman, etc) before the theme actually loads. Then, once the page finally does load, some of the lines of the table extend too far and show when they shouldn't. Only after refreshing the page (and the half-second half-second "no theme" period that follows) do I finally see the page as it was meant to load.

I have this problem only on Firefox on this computer. It works fine on Internet Explorer on this computer, as well as on all browsers on other computers I tried. I've cleared cache, cookies, history, etc, but I still have this problem.

Any ideas?
Thank you.