Safari version: make findings panel a popover instead of an iframe

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It would be great if the findings panel would be implemented as a popover (see https://developer.apple.com/library/s...).

- It would be more visually consistent with the Firefox version.
- It won't alter the page's DOM, thus reducing the potential for breaking sites.
- It would look much nicer and integrate better with the OS X look and feel.

The only downside is that popovers require Safari 5.1, but it is available even for Snow Leopard users, so there's no compelling reason to support 5.0.1 anymore.