The line afterLabel.textContent = ""; causes the anonymous content including the <children> element to be removed. This causes problems with the patch in bug 653881 as this handles insertion points and default content differently. A simple fix is to just move the <children> element outside of the <span>.

Comment on attachment 620291 [details] [diff] [review] updated patch with fixed test The old binding really confuses DOM Inspector, it doesn't seem to know what's going on ;-) >+<?xml-stylesheet href="data:text/css,k { display: inline; text-decoration: underline; }" type="text/css"?> u would be too confusing, I suppose? + <label control="b5" maxwidth="50">Quite a <k>l</k>ong label. Hopefully it will wrap"</label><textbox id="b5" label="Button5" size="2"/> Nit (×4): was the " after wrap an oversight? >\ No newline at end of file Nit (×2) >- <html:span anonid="accessKeyParens"><children/></html:span> >+ <children/><html:span anonid="accessKeyParens"></html:span> Remove the comment about setting .textContent too, I guess?

Please can you set the milestone when landing on inbound. Thank you :-) https://hg.mozilla.org/mozilla-central/rev/d3733e739f16