Discovered last week: @.supports (transition-property: nonsense) returns true in Chrome. But Chromium 34 and below return false.
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I found a false positive in Firefox @support {appearance: none} in version 33. The browsers really need to be careful with that.
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I think the issue you're seeing is that we've had to add more behaviors to -moz-appearance:none, copying other browsers.
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You can't test for a specific effect that it has, only whether it's accepted, which should mean it does something (it did)
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The 'appearance' property specifically is a mess; there's no spec for form controls or how 'appearance' affects them.
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Replying to @davidbaron @jnowland @ppk
So we end up having to copy different behaviors from other browsers at different times. @supports won't help there.

Jul 6, 2016 路 2:44 AM UTC

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Replying to @davidbaron @jnowland @ppk
In Fx33, <select> w/ & w/o -moz-appearance:none are different (use system theme vs. not, general behavior of appearance).
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There was a later change to remove the dropdown from the without-system-theme version, for compat with other browsers.
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more replies
Replying to @davidbaron @ppk
this makes a lot of sense but is hard to communicate to web-devst hat aren't across the the nitty gritty details :/