This is a somewhat obscure problem that only occurs with some templates when using the JCK editor. It is related to the template but I've never isolated excatly which styles are causing the issue. It only happens in Firefox.
If you use Firefox when using JCK to edit a site, you may find that the screen jumps to the top of an article when you first click on it to start editing. This only occurs if you use the scrollwheel on your mouse to scroll down through the article. It doesn't happen in other browsers and it only happens the first time you click on the article and it won't happen if you use the scroll bars to scroll down through the article. So, it's a somewhat obscure bug that is easily avoidable but I thought I'd mention it because it drove me crazy for weeks before I isolated the cause.