In Firefox, radiobuttons with `required` and `v-model` are marked as invalid immediately

[ThomasLandauer]

Version

2.6.11

Reproduction link

https://jsfiddle.net/t1po5sdh/

Steps to reproduce

In Firefox 75.0, I get the two radio buttons marked as invalid (i.e. surrounded by a red border) immediately on pageload. This does not happen if I either remove required or v-model

What is expected?

The radios should only be marked as invalid after form submission - as with other required input controls.

What is actually happening?

See above

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I've been observing this for years already.

[posva]

This seems to happen in js as well as soon as the property checked is touched: https://jsfiddle.net/Lz5u2wah/ which we need to do for v-model

[unbyte]

Firefox will mark the required radio input with a red border if you had operated the radio input without giving it a selected value.
I guess vue had set the property checked of all the radio inputs to false when it created data bindings because of null, then the radio inputs had been marked as invalid by firefox.