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Firefox has two features that let you see how much memory and CPU resources are being used by tabs, extensions and other processes: Process Manager and Task Manager. These features can be useful for diagnosing and solving high memory or CPU usage in Firefox.
Firefox has a feature that lets you see how much memory and CPU resources are being used by tabs, extensions and other processes. This Process Manager feature can be useful for diagnosing and solving high memory or CPU usage in Firefox.
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Process Manager
To open the Process Manager, click the menu button 
, click and select from the menu. The about:processes page will open in a new tab.
You can also enter about:processes in the address bar or use the keyboard shortcut Shift + Esc to open this page.
Information in the Process Manager
Information is displayed in multiple columns:
- Name: A list of processes that Firefox is running and ID numbers that identify each process. For technical information about process types, see the Process Model – Firefox Source Docs documentation.
- Memory: A rough estimate of how much computer memory each process is using.
- CPU: A rough estimate of how much of your computer's processing power each process is using.
- (gear icon): This column displays an action button when you hover over an item, to allow actions such as closing a tab or killing a process.
You can click on the Memory or CPU headers to sort the list in descending order. Click again to reverse the order.
Perform actions in the Process Manager
Hovering over an item in the Process Manager can show a profiler icon next to it's name and ID. The action button will also appear on the right side.
You can use the profiler icon to evaluate a process performance. It will start recording a profile, gathering data from all threads of the process for 5 seconds, and then will launch the Firefox Profiler in a new tab showing the recorded profile.
The action button can be used to close a tab or leave it open but unload its contents and kill associated processes.
Task Manager
The Task Manager displays useful information about the tabs and individual add-ons actively running on Firefox.
To open the Task Manager, enter about:performance in the address bar. The Task Manager about:performance page will open in a new tab.
Information in the Task Manager
Information is displayed in multiple columns:
- Name: The name of the tabs and extensions currently running within Firefox. Extension IDs will also be included in this column.
- Type: Whether each item is a tab or an add-on. Some tabs have additional subtasks, that may include subframes, trackers or service workers associated with the tab.
- Energy Impact: The CPU processing power being used by each task. Tasks with a higher energy impact will drain your battery quicker and may slow down the performance of your system.
- Memory: The amount of RAM each task is using on your system.
You can click on any column header to sort the list. Click again to reverse the order.
View subtasks
Some tabs have additional subtasks that can be viewed from the Firefox Task Manager. These may include subframes, trackers or service workers associated with the tab.
To view subtasks, select the right-arrow on the left side of the task's name. You can hide the subtasks again by selecting the down-arrow on the left side of the main task's name.
Perform actions in the Task Manager
Hovering over an item in the Task Manager will show more details about the performance of this tab or extension. The action button will also appear on the right side of the task.
The action button can perform the following on:
- Tab Tasks: Close the associated tab.
- Add-on Task: Open the add-on page in a new tab.
