The JSON Section showing JSON preview of WS frames is using the Tree component (JSONPreview). This component has support for expanding long strings, which should be disabled in this case.

Honza

Here is what we should do:

diff --git a/devtools/client/netmonitor/src/components/websockets/FramePayload.js b/devtools/client/netmonitor/src/--- a/devtools/client/netmonitor/src/components/websockets/FramePayload.js
+++ b/devtools/client/netmonitor/src/components/websockets/FramePayload.js
@@ -164,16 +164,17 @@ class FramePayload extends Component {
         labelledby: "ws-frame-rawData-header",
         opened: true,
       },
     ];
     if (!isTruncated && this.state.isFormattedData) {
       items.push({
         className: "formattedData",
         component: JSONPreview({
+          expandableStrings: false,
           object: this.state.formattedData,
           columns: [
             {
               id: "value",
               width: "100%",
             },
           ],
         }),