Quick hits for spec compliance

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https://bugzilla.mozilla.org/show_bug.cgi?id=1337702 (from PM1117)
URI.toJSON()

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Let's take this over as a general "quick hits spec compliance" issue.

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https://bugzilla.mozilla.org/show_bug.cgi?id=1203668 (from PM1125)
changing the value of a select to a value that matches none of the options should put it in a "no option selected" state even when it's a combobox (size=1)

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https://bugzilla.mozilla.org/show_bug.cgi?id=1265136 (from PM1129)
new Date(<mm/dd/yy>) behaves differently in Firefox vs Chrome/Safari

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https://bugzilla.mozilla.org/show_bug.cgi?id=1270451 (from PM1128)
A Blob URL object's origin property should not be "null"

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https://bugzilla.mozilla.org/show_bug.cgi?id=1274526 (from PM1127)
Support 'q' absolute length units from CSS3 values and units

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https://bugzilla.mozilla.org/show_bug.cgi?id=1346936 (from PM1164)
Support "SourceMap" header (basically fix header name)

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https://bugzilla.mozilla.org/show_bug.cgi?id=1256299 (from PM1263)
Reenable isSameNode()

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https://bugzilla.mozilla.org/show_bug.cgi?id=1259459 (from PM1264)
Fix HTTP/2 OPTIONS

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Various CSS selector improvements (PM1268)
DOM scrollingElement (PM1267)
fix maxlength (PM1114)