Luis & RESN,
Very sorry for not responding to this earlier. It's been on our 'to-do' list for investigation, but slipped due to some other priorities concerning our upcoming release. Let's see what we can do to help!
First off, this issue isn't something we've heard of before, so it may be something pretty-specific to your site. One thing I would definitely recommend, and which may immediately fix, the problem is to switch from the Javascript button to a static image. We don't have an 'easy-tag' like {JFBCLogin} to do so, but you can easily insert one with the following HTML:
<a href="javascript:void(0)" onclick="jfbc.login.login_custom();"><img src="/linktoimage.jpg" /></a>
That has the advantages of not using Javascript loaded from Facebook which is both faster and less prone changes or issues caused from their Javascript. The disadvantage is that you need to create an image (you can just take a picture of the normal Login with Facebook button) and that the text is not translatable.
If you're using the SCLogin module, there's an option in their for the Login Button Type. Just change that to "Image" and add the link to the image you want to use below it, and hopefully that will fix you up.
If you're still having issues, or I missed a case that you're using, just let us know!
Again, sorry for the delay, and we'll be much more responsive to requests in this post going forward!
Thanks,
Alex