Firefox provides command URLs so that a user or developer can see some internal information about the browser. They serve as a diagnostic and troubleshooting tools when developing websites, especially when developing for advanced features of browsers like IndexedDB, Service Workers, etc.
URL Format
These pages can be accessed by typing the corresponding URLs in the Address Bar. The URL format is ‘about:’ following by the page name. An example is given below:
Type this into the address bar of the Firefox browser and it should show the Preferences page.
Complete list of Firefox about: pages
Below is the complete list of all available Firefox about: pages:
[table id=2 /]
These pages are incredibly useful during development of advanced functionality for a webpage.