Hi,
I set zh-hk (Chinese/Hong Kong) as my most preferred language in Firefox. When I browse any generated Page Shot URL like https://screenshots.firefox.com/YnyWizx6ulrPZ23e/null, the interface is in Simplified Chinese, which is used by Mainland China, but not Hong Kong. It should be traditional Chinese for Hong Kong.
In addition, I never tested it but some other Mozilla products may have the same problem of setting Simplified Chinese for zh-hk so developers may want to look into that as well.
Although Simplified Chinese and Traditional Chinese do look quite similar, it would be great if developers can take some times to resolve the problem. Thanks.