plone/plone.app.toolbar — comment on commit 15c8f0e47db8c7fbe68012519c18bcbae7147c28
File:  line 0
By lrowe:

If you don't have javascript enabled then you shouldn't see the iframe at all, you only want the link. So adding the iframe with Javascript makes sense to me. It also helps keep the page as small and semantic as possible.