[Theme: Scrappy] Links not working properly

I started to use this beautiful theme Scrappy a few weeks ago and discovered an odd problem with links. It does only persist while using Firefox and IE, everything is working fine with Google Chrome. Whenever I do click on one of the links on my site, the characters of the link make an awkward jump. If I do click a second time on the link, I’m finally referred to the target of the link. This also appears when I click on any headlines. I wonder why that happens? I have disabled all plugins and cleared the browser cache but the link behaviour does not change in Firefox.

I must confess that I made a few changes to the theme, so it is possible that this is entirely my fault. Nevertheless I hope that somebody can give me a hint about what’s wrong and how to fix it. Here’s the link to my blog:

http://www.lieinthesound.de/

Thanks so much in advance!