Admin Page: warnings when updating modules in Firefox

[jeherve]

Steps to reproduce

1. Start with a site that's connected to WordPress.com.
2. In Firefox, go to Jetpack > Settings
3. Try enabling or disabling modules
4. You'll get the following warning:

“jetpackState[module]” will be soon rejected because it has the “SameSite” attribute set to “None” or an invalid value, without the “secure” attribute. To know more about the “SameSite“ attribute, read [https://developer.mozilla.org/docs/Web/HTTP/Headers/Set-Cookie/SameSite](https://href.li/?https://developer.mozilla.org/docs/Web/HTTP/Headers/Set-Cookie/SameSite)
Cookie “jetpackState[error]” has been rejected because it is already expired.

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Original report:
p8oabR-QB-p2#comment-6303

[anomiex]

Looks like this is mostly a bug in Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=1653518

The TL;DR is that Firefox wants to change their default when SameSite is not specified (from "None" to "Lax"), and then start rejecting cookies with "SameSite=None" and lacking "Secure". We're not specifying SameSite at all, so our cookies won't be rejected as the warning claims because the defaulting to "Lax" instead of "None" will happen first. But Firefox's warning isn't taking that into account, so it's whining about the defaulted-to None.