Yahoo email acting quirky

I use Avast free Antivirus 7.0.1426, Windows 7, IE 9. A few months ago my Yahoo email started acting quirky. Frequently, when I try to open an email, a tab opens which has the correct subject in it, however the body of the email either fails to appear (unless I hit reply or forward), or the body of a different email from my inbox appears. It doesn’t happen on our desktop, only on my laptop, so I don’t think it’s a Yahoo problem. So I was wondering if it might be an Avast problem. Can you help? Thanks.