I just recently re-installed Digg Digg because I can't find any other plugin to suit my needs. Now, I just found out that the floating bar is not showing up on Firefox for my blog.
I handle another blog and that one doesn't have the same issues with displaying the floating bar on the single post page. Digg Digg shows up even on Firefox. I tried disabling my plugins one by one to see which one has conflicts with Digg Digg, but none of them seem to be the problem.