Created attachment 8732044 [details] testcase ###!!! ASSERTION: Shouldn't return empty rect: '!mTmp.IsEmpty()', file nsRegion.h, line 375
The box has x1 = -180, x2 = 2147483580, so when it's converted to a rect the width is x2-x1 = 2147483580 + 180, which overflows negative since these are signed 32 bit ints. And negative widths are interpreted as empty.
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