This is definitely not fun
We use Macs too, almost exclusively actually, for development. Below is a picture of what I'm seeing in Safari:
The overflow:hidden you're seeing is actually buried within the Facebook iFrame for the send button. That's too far 'in' and that's not the problem. If you want to find the right div, it will be outside of the fb:like tag itself. Additionally, you want to find a div where the blue outline *exactly* lines up with what's getting cut-off. The blue outline in your picture is actually to the right of it. If the contents extended that far, as they should, the overflow:hidden wouldn't have an effect since there wouldn't be anything extending past the blue box. From your picture and looking at your html, it would look to be either #midblock or .insidem Neither of those have z-index's or overflow:hidden properties that I see though, so not sure what's causing that to get cut-off for you.
As for clicking the Like button, that too works perfectly for us:
What is the exact error message you get? Does that happen with other users? Are you logged into Facebook and have the "Use Facebook As" setting enabled so that you're browsing as your Facebook Page instead of your personal profile? Since the counts are showing something on the Like buttons, it means that others have been able to make it work..
Finally, for the different Facebook Like counts, each Like button is tied to a unique URL.. either the URL of a page on your site or your Facebook Page. Each URL has it's own individual Like count, so the Page count will be different than the count of Like's for individual pages of your site.
Hope that all explains. No clue why we're seeing completely different things, but check those divs I mentioned above and see if you're seeing overflow or z-indexs that I'm not. Also, clear your browser cache (again), if you haven't recently.
Thanks,
Alex