If I try to access statistics data for an extension where this data is not public (see URL above for example) I get an error page - served as plain text. Same goes if I open https://addons.mozilla.org/en-US/firefox/statistics/csv/. Apparently everything in this "directory" is served as plain text - error page or not.
Not super important since the only way to get this bug is to tamper with the URL, but will fix for 3.2.1 anyway.
Fixed in r11859.
https://preview.addons.mozilla.org/en-US/firefox/statistics/csv/ is served as text/html, as is https://preview.addons.mozilla.org/en-US/firefox/statistics/csv/10/application Verified FIXED