Eugene added proper rendering of ES6 classes in the console and debugger (bug 1592277)
Instant Evaluation keeps getting better
Oriol added support for Proxy and Reflect methods in bug 1615861
Logan added support for side-effects free DOM method (like querySelector for example)
Highlight DOM element results (bug 1614549)
Fixed issue with autocomplete case-insensitive matching in bug 1614841
[WIP] Display the autocomplete above the input so it doesn’t cover the instant evaluation result (bug 1609942)
Alex made the Browser Toolbox Console faster to open (bug 1605763)
Console should be faster when dealing with lots of new messages at once (bug 1612571)
Added autocompletion support for optional chaining operator (?.) that landed in Firefox 74 (bug 1594009)
Bug 1614567 - Add borders between columns in network requests list
The Network panel introduced nice column borders for better readability.
Temporary extensions loaded in GeckoView apps now also appear in about:debugging when connected to the device. Implemented by Luca Greco in bug 1596867.
Historically, the framework part of the code that deals with client to server communication for DevTools has been called DebuggerClient and DebuggerServer.
This likely comes from the fact that the Debugger was probably the first tool to be based on a remote (client-server) architecture.
These objects have now been renamed to the more self-explanatory DevToolsClient and DevToolsServer.