Created attachment 8898055 [details] testcase 1 I've managed to reduce out a testcase showing the rendering differences causing welt.de's mobile search bar to render differently in Firefox and Chrome (see webcompat.com bug #8294 for screenshots/etc). I'm not sure what combination of factors is causing the issue, so I've attached the testcase. dholbert, I see flexbox may be involved, so I've cc'd you here as well. I'm not sure if it's the only factor, however.
Attachment #8898055 - Attachment description: testcase.html → testcase 1
Created attachment 8898395 [details] testcase 2 Here's a more reduced testcase, with several examples for comparison. In some intrinsic-sizing cases (latter 2 examples in this testcase, inline-table and floated table), both Chrome and Firefox handle percent sizes on table-cells by "back-computing" an appropriate intrinsic size for the table as a whole. BUT, Firefox does not seem to trigger this back-computing behavior if the table is inside of a block that's being intrinsically-sized. We only do it when the table itself is being directly intrinsically-sized. This seems like a bug, though tables are quirky and under-specified...
EXPECTED RESULTS for testcase 2 (based on webcompat & intuition if nothing else): All 4 tables should be the same width (~10x the width of the "a", back-computing from "10%"). ACTUAL RESULTS: First two tables are skinny (they shrinkwrap the a's width). Every other major rendering engine has "expected results" -- I tested Edge 15, IE 11, Chrome 60, Safari 11, and Opera 12.15 (Presto). Whereas, Firefox 57 (current Nightly) has "actual results".
Component: Layout → Layout: Tables
Summary: Test case derived from www.welt.de does not render consistently in Firefox and Chrome → tables back-compute their intrinsic sizes inconsistently (only when they're being *directly* intrinsically sized, but not inside intrinsically-sized container)
Summary: tables back-compute their intrinsic sizes inconsistently (only when they're being *directly* intrinsically sized, but not inside intrinsically-sized container) → tables inconsistently back-compute their intrinsic sizes from percent-sized cells (only when they're being *directly* intrinsically sized, but not inside intrinsically-sized container)
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