I am a back-end developer (API maintainer) and I use firefox as my primarily browser at work. A feature that I would find very useful would be that firefox prettifies the "Form Data" under the "Request" tab when a request is selected under the "Network" tab in the developer tools, and by prettify I mean to display in multiple lines and highlighted properly (for a comparison example you can take the "Postman" application feature under the "raw" tab).
As of now it only displays the form data in a single horizontally scrollable line and it also has a "Raw" toggle.
Thank you and keep up the good work.