Thanks Jonathan. Somehow that Mozilla bug escaped my attention for five years! I'll add code to reject GDEF table based on its length and glyph class of doublequote. Do you have any more blacklisted tables like that in Firefox? behdad <div class="gmail_quote">On Feb 24, 2016 11:17 PM, "Jonathan Kew" <<a href="mailto:jfkthame@gmail.com">jfkthame@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">On 24/2/16 02:25, Behdad Esfahbod wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> Hi Jonathan, As you probably know, I changed mark zeroing from BY_UNICODE_LATE to BY_GDEF_LATE in HarfBuzz. So far I only got a bug report about Cantarell breaking, which was fixed in the font's GDEF table. Today, Dominik and I noticed that Times New Roman Italic on Windows 7 has wrong GDEF class for ASCII double-quote, and as such, we now zero its advance width. The bug is not present in Windows XP or Windows 8 on. It also happens to be present on the OpenType Times New Roman Italic on OS X, but that is superseded by a non-OpenType version of the font. Even with the broken font, CoreText does not show the bad rendering, whereas, in my testing, Uniscribe from Windows 7 does. Given that Windows 7 still has the largest market share across PCs, I feel like we cannot ignore this. I assume IE probably does not expose this bug because they don't process OpenType features for Latin? Can someone test on Windows 7? </blockquote> I don't have a test system handy just now, but I believe you're correct. <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> I'm not sure how to proceed forward. IIRC we have had also observed one Latin glyph with wrong GDEF back a few years ago, in Georgia or some other font on Windows. That should be in mozilla bug tracker somewhere. </blockquote> See <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=589682" rel="noreferrer" target="_blank">https://bugzilla.mozilla.org/show_bug.cgi?id=589682</a> for the Times New Roman Italic GDEF bug. (We added a hack in Gecko to ignore the GDEF for that particular font.) JK </blockquote></div>