Mozilla plans to enable a new feature called Process Priority Manager in Firefox 69 Stable later this year. The organization began to integrate the feature in Firefox Nightly about a year ago and has tested it thoroughly in that time.
The idea behind the feature is to deprioritize background tabs open in the Firefox browser so that the active tab (foreground tab) may have additional resources at its disposal. Firefox's new process priority management feature won't impact background media processes as playback quality might suffer otherwise.
Firefox will give Windows hints to appropriately set content process priority levels, meaning more processor time spent on the tasks you're actively working on, and less processor time spent on things in the background (with the exception of video and audio playback).
Process Priority Manager is already enabled in Firefox Nightly. The feature is controlled by a preference that users of the browser may change to enable or disable it. The preference will be available in all versions of Firefox; while it is generally not recommended to disable the Process Priority Manager, some may need to do so if they run into issues when it is enabled on their devices.
Mozilla ran some tests and concluded that the "process priority manager had no measurable impact on page load time, tab switch time, or user retention". The organization's test did not make things better, however, in test scenarios either.
It is possible, however, that the results may be positive in low resource environments.
Do this to change the value of the Process Priority Manager:
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