https://jsfiddle.net/dgrogan/odmzzwdz/

<table style="border-collapse:collapse; border:1px solid blue" >
    <tr style="border:18px solid yellow" id="row">
        <td style="border:2px solid lime" />
    </tr>
    <tr>
        <td/>
    </tr>
</table>

Table is 86px wide. But changing #row's border to 4px leaves the table at 86px wide instead of changing to 58px.

Edge gets it right. Chrome and FF get it wrong in different ways.

Found while looking at fast/table/border-collapsing/cached-change-row-border-width.html