User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:2.0b6pre) Gecko/20100901 SeaMonkey/2.1b1pre
The extenders for hookleftarrow, hookrightarrow and mapsto are borked in Seamonkey (see the screenshot). Firefox is better, thought it stretches the characters hookleftarrow, hookrightarrow, rather than extending them (see the screenshot).
Created attachment 472910 [details]
Created attachment 472911 [details]
Rendering in Seamonkey nightly
Created attachment 472912 [details]
Rendering in Firefox nightly
E10B "stix-extender for horizontal solid (normal) arrow", which was in STIX Beta is not in v1.0.0. I wonder what the intended replacement was.
U+23AF HORIZONTAL LINE EXTENSION maybe.
Created attachment 488691 [details] [diff] [review]
Comment on attachment 488691 [details] [diff] [review]
I would be good to get this very confined change into Gecko 2.0 as more and more people will be moving to STIX v1.0.0 fonts.