So Firefox 106 triggered a bug on 1st gen Ryzen processors. We found this by noticing a bunch of nonsensical crashes in the painting code that only happened on these processors.
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How did we fix it? By rebuilding the exact same code as 106. The timing differences caused by using a new profile when doing PGO were enough to cause the generated code to be different enough to avoid triggering the processor bug.
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What actually is the processor bug though? Even if a crash only shows on one processor type my first assumption would be unlucky timing exposing an application bug / UB.
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We don't know what the actual bug is yet but are talking with AMD about it.
bugzilla.mozilla.org/show_bug.cgi?i has some details about why the crashes don't make sense.