Created attachment 8811878 [details] Minimized example showing the issue in FF, but not in Chromium User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:49.0) Gecko/20100101 Firefox/49.0 Build ID: 20161025170457 Steps to reproduce: Open the attached minimized example. Tested on Firefox 49.0.2 Firefox Developer Edition 51.0a2 (2016-11-14) (64-bit) Firefox Nightly 53.0a1 (2016-11-17) (64-bit). Firefox for Android Beta 50.0b12 Actual results: The outermost divs (blue and red) keep the same width as if the yellow one did not have width set, which you can verify by toggling the "width: 100%" in the element inspector/firebug. Also if the "position: fixed" is removed from the blue, the expected behavior appears. Expected results: The blue, the red and the yellow div should be stretched to fit the width of the viewport.
Created attachment 8813297 [details] slightly simpler testcase
Attachment #8811878 - Attachment is obsolete: true
Presumably this relates to how we compute the intrinsic preferred width (PrefISize) of the table. I think we should be reporting an infinite result in this case, but we don't seem to be. Edge matches Chromium.
Component: Layout → Layout: Tables
Summary: div table width wrong in a fixed div → intrinsic width of table that contains a 100% width cell and other things should be infinite, but isn't
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