What version are you running?
3.0.1
What's the URL of the page containing the problem?
...../r/42/_fragments/diff-comments/123,234,345/?allow_expansion=1&123445345
What steps will reproduce the problem?

have diff with unicode content
make comment for fragment with unicode text
get js error on ...../r/42/ for all fragments after fragment with unicode content


What is the expected output? What do you see instead?
doesn't matter
What operating system are you using? What browser?
doesn't matter
Please provide any additional information below.
html payload size return bytes not a symbol count

https://github.com/reviewboard/reviewboard/blob/d41ea146f5152792961a8e00e08df4b80cf14334/reviewboard/reviews/views.py#L1430
fixed by change len(html) to len(html.decode('utf-8'))