The Response panel doesn't render when looking at the POST request generated by the attachment for Bug 1344511, https://bug1344511.bmoattachments.org/attachment.cgi?id=8843629. When clicking the Response-tab, whatever that is rendered in the panel below stays, as a re-render is not performed. It won't render because of a "TypeError: mimeType is undefined" on this line http://searchfox.org/mozilla-central/source/devtools/client/netmonitor/shared/components/response-panel.js#121 and `mimeType` is explicitly set to undefined here http://searchfox.org/mozilla-central/source/devtools/shared/webconsole/network-monitor.js#607 For some reason, for that particular POST, `this.request` does not implement(?) the required interface. `nsIChannel` I believe.
Thanks for reporting this issue. I can reproduce the issue in Nightly with https://bug1344511.bmoattachments.org/attachment.cgi?id=8843629.