Firefox Relay Service and Unicode escape sequence.

That's what I get:
\u0417\u0434\u0440\u0430\u0432\u0441\u0442\u0432\u0443\u0439\u0442\u0435
It's "Hello" in Cyrillic.

--UPD--

It was "Body" of email. Google Mail.
Also, answer notification came to me directly to my main mail (not relay) and contains this:
We & #39 ;re
and
& quot; From & quot;, & quot;Subject & quot;, or & quot;Body & quot; of the email?

Idk is that google, mozilla or both.