User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:65.0) Gecko/20100101 Firefox/65.0

Steps to reproduce:

Open large JSON file with network response tab open, like this:

1. Open Network panel in Devtool
2. Go to a large JSON file. I used http://api.nobelprize.org/v1/prize.json.
3. Look for the JSON file and select it. Filter by JS if you can't find it.
4. On the right hand side, select Response tab.

The process is the same for XML. An example link I use is https://www.omg.org/spec/CWM/20020501/02-05-01.xml.

Actual results:

For JSON files, Response tab should have 2 panels: JSON and Response Payload. However, for large file, the JSON panel gets so long vertically, it pushed any remaining panel out of view, so user may not realize there are additional panels.
The JSON example I provided is not horizontally wide enough to have the horizontal scrollbar missing, but the XML one do. When viewed in the Response Payload for that XML file, text on the right side get scut off. The panel would need to be scrolled to the bottom before a horizontal bar is visible.

Expected results:

The horizontal scrollbar should be visible without user having to scroll all the way to the bottom. In file types that can result in 2 panels like JSON, both panel should be visible.

Some of the earlier attempts of this work can be found at bug 1498565, including a codepen demo of what it should look like by Florens Verschelde at https://codepen.io/anon/pen/bOEpVZ in comment 14.

Thanks for the report Amy!

Honza

Just encountered this issue as well, updating and attaching a recording for better visibility.