I saw this warning while trying to login to Youtube ......Please tell me what this means

[security_matters]

I saw thing warning today when I was trying to log in to my Youtube account.
What does this mean ? I selected "Always block".
Never saw this message before so I am worried.

[barbaz]

According to https://www.google.com/supported_domains both sites in that message are Google domains, and they're both the Google accounts/sign-in site, so I would say this is not really "cross-site" and therefore is safe to allow. I also don't see offhand anything that looks like XSS in the visible portion of that URL.

[security_matters]

I didn't know NoScript too gives false positives. Thanks.