User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:55.0) Gecko/20100101 Firefox/55.0 Build ID: 20170814072924 Steps to reproduce: 1)open the debugger an select Network tab 2)then select one of the requests in the list. 3) the side panel that normally lists Headers, Cookies Params, Response, Preview, Timings is missing in the Preview Tab. Actual results: When I opened the network tab in the debugger to check what was causing a 500. Upon selecting the request that had a 500 error the I noted that the preview tab was missing. This behavior was also Observed even if the Status on the request was 200. There is however a new stack Trace Option. Expected results: Their should be a Preview option.