Home page links in sidebar second not clickable in firefox or chrome

I have a clearfix div containing columns loaded into the home page content with sidebar second active with the user login box.

Nothing in the sidebar is clickable in firefox or chrome until the sidebar content is below the home page content, i.e. the home page content container seems to overlay the sidebar even though the actual text does not.

This is fine in IE, and also is fine as soon as I log in (via ?q=user). Once logged in everything on the home page sidebar is clickable in firefox and chrome.

using a left sidebar instead of right overcomes this issue but I don't want the left sidebar content appearing on phones etc. before the main page content.

I have tried a variety of z-index settings but no luck, again this occurs only when no user is logged in.

Any suggestions?
Thanks :)