Testing on Release/Beta, favicons aren't being shown for domains with IDN unicode domain names. Somewhat ironically, because of bug 1380617 this is currently working on Nightly (because all IDN domains are shown in plain Punycode), but my patches for bug 1391421 will most probably break this again.
I just noticed that after dropping a rather speculative set of favicon-related changes from my patches for bug 1391421 (https://hg.mozilla.org/try/rev/204e8544b1f33ccbd993b736b0398925924c8047), favicons now seem to work for IDN domains as well. At the moment I've got no idea why that is so, although at least it's still a nice surprise.
Status: NEW → RESOLVED
Last Resolved: 8 months ago
status-firefox56: fix-optional → wontfix
status-firefox57: affected → unaffected
Resolution: --- → WORKSFORME
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