Deprecated tools - Firefox Developer Tools
webide and connect page webide was deprecated as of firefox 69 disabled as of firefox 70 (bug 1539451).
... description webide allowed you to connect the firefox developer tools to remote browsers, such as firefox for android.

Using the Browser API
to run the demo, the best approach is to clone the github repo locally (or just download it directly if you don't do github), open webide, open the repo as a packaged app, then run it either on a simulator or a real device if you have one.

Memory Profiler
using the add-on open the devtools panel or webide.

All keyboard shortcuts - Firefox Developer Tools
+ e ctrl + shift + e toggle responsive design mode ctrl + shift + m cmd + opt + m ctrl + shift + m open browser console ctrl + shift + j cmd + shift + j ctrl + shift + j open browser toolbox ctrl + alt + shift + i cmd + opt + shift + i ctrl + alt + shift + i open scratchpad shift + f4 shift + f4 * shift + f4 open webide shift + f8 shift + f8 * shift + f8 storage inspector shift + f9 shift + f9 * shift + f9 open debugger 3 ctrl + shift + z cmd + opt + z ctrl + shift + z 1.