Developers at Mozilla have decided to remove the "about:performance" utility page, which allows users to track the CPU load and memory consumption generated while processing various pages. This decision is due to the introduction of the "about:processes" interface starting from Firefox 78, which duplicates the functionality of "about:performance" but is considered more user-friendly and informative.
For example, the "about:processes" page not only shows the titles of the pages but also links tabs and sub-resources to domains, as well as provides information on resource consumption by background processes and workers. Among the advantages of the soon-to-be-removed "about:performance" is the ability to separately track resource consumption by extensions. The "about:performance" interface is already called by default when selecting the "More Tools -> Task Manager" menu. After its removal, any attempt to open this utility page will result in the display of the "about:processes" interface.
Source: opennet.ru
