The relevant definition in the spec;
https://drafts.csswg.org/css-device-adapt/#min-scale-max-scale
Before this change, if both of initial-scale and maximum-scale are negative,
both values are clamped to 0.25. Whereas with this change, negative scale
values are treated as if it's not specified so that initial-scale value is
automatically calculated based on the layout viewport size.
negative-initial-and-maximum-scale.html is a test case for the case.
Also with this change, initial-scale values are going to be clamped to the
range [0.25, 10] during parsing it so that initial-scale-0.html and
initial-scale-100.html need to be modified, now the former is scaled by 0.25x,
the latter is scaled by 10x.
(Before this change, initial-scale=0 and initial-scale=100 were treated as
invalid scale values in nsViewportInfo::ConstrainViewportValues[1])
[1] https://searchfox.org/mozilla-central/rev/6c9f60f8cc064a1005cd8141ecd526578ae9da7a/dom/base/nsViewportInfo.cpp#15,19
Differential Revision: https://phabricator.services.mozilla.com/D32098
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extra : moz-landing-system : lando
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