I filed bug 1766530 for the first case in the attached testcase (width:auto) where Firefox is getting things wrong. I included a clearer testcase over there. Beyond that, this bug was me just misunderstanding things, for reasons discussed in comment 5 - comment 6. --> closing this out as INVALID.
Bug 1765664 Comment 7 Edit History
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I filed bug 1766530 for the first case in the attached testcase (the part with the width:auto abspos thing) where Firefox is getting things wrong. I included a clearer testcase over there. Beyond that, this bug was me just misunderstanding things, for reasons discussed in comment 5 - comment 6. --> closing this out as INVALID.