Greycliff (and other) font cross browser baseline / vertical alignment consistency problem
After much searching, from what I can tell this is a issue with the font files vertical metrics and I don't know how to go about reporting / getting this fixed.
It's not the first time I've noticed this problem with typekit fonts, it would be great to have some sort of quality control taken to assure this doesn't happen.

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Thanks for reporting this issue and for your detailed observations.
The baseline/vertical alignment inconsistencies were due to the font files vertical metrics. We have addressed the issue, and it has now been shipped.
To see the improvement, please re-publish your webfonts in your Typekit kit. This will ensure the updated metrics are applied across browsers.
We appreciate your patience and commitment to quality. Please don’t hesitate to contact us if you notice anything else!
Thanks,
Adobe Fonts Team