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    <body><span class="vcard"><a class="email" href="mailto:karl+webkit@la-grange.net" title="karl <karl+webkit@la-grange.net>"> <span class="fn">karl</span></a>
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          <a class="bz_bug_link 
          bz_status_UNCONFIRMED "
   title="UNCONFIRMED - webkit doesnt render frame border"
   href="https://bugs.webkit.org/show_bug.cgi?id=21697">bug 21697</a>
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            <th>What</th>
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           <td>karl+webkit@la-grange.net
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            <b><a class="bz_bug_link 
          bz_status_UNCONFIRMED "
   title="UNCONFIRMED - webkit doesnt render frame border"
   href="https://bugs.webkit.org/show_bug.cgi?id=21697#c3">Comment # 3</a>
              on <a class="bz_bug_link 
          bz_status_UNCONFIRMED "
   title="UNCONFIRMED - webkit doesnt render frame border"
   href="https://bugs.webkit.org/show_bug.cgi?id=21697">bug 21697</a>
              from <span class="vcard"><a class="email" href="mailto:karl+webkit@la-grange.net" title="karl <karl+webkit@la-grange.net>"> <span class="fn">karl</span></a>
</span></b>
        <pre>Created <span class=""><a href="attachment.cgi?id=444636" name="attach_444636" title="Rendering in Edge Blink, Firefox Gecko, Safari WebKit">attachment 444636</a> <a href="attachment.cgi?id=444636&action=edit" title="Rendering in Edge Blink, Firefox Gecko, Safari WebKit">[details]</a></span>
Rendering in Edge Blink, Firefox Gecko, Safari WebKit

Here a better test with the different renderings in different browsers. 

<a href="https://html.spec.whatwg.org/multipage/rendering.html#attributes-for-embedded-content-and-images">https://html.spec.whatwg.org/multipage/rendering.html#attributes-for-embedded-content-and-images</a>

Suggested CSS
iframe[frameborder='0'], iframe[frameborder=no i] { border: none; }

Unclear case:

frameborder='' 
* no border in WebKit/Blink
* border in Firefox.</pre>
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