Guide to Unloading Tabs on Firefox's about:unloads Page

This article provides a quick and clear walkthrough on how to use the built-in about:unloads page in the Mozilla Firefox web browser. You will learn how to access this hidden system page, understand the exact priority order Firefox uses to discard inactive tabs when system memory runs low, and how to manually trigger the tab unloading process to free up RAM immediately.

Accessing the about:unloads Page

To view your tab memory usage and unloading priority, you need to access an internal Firefox page:

  1. Open the Firefox web browser.
  2. Click on the address bar at the top of the window.
  3. Type about:unloads and press Enter.

Viewing the Tab Discard Priority Order

Once you are on the about:unloads page, you will see a table displaying all your currently open tabs. Firefox uses this table to determine which tabs to put to sleep first when your computer starts running out of memory.

The table is organized by the following metrics to determine priority:

  • Priority: The tabs are listed in the exact order they will be unloaded. The tab with a priority of 1 is the very next tab that Firefox will discard. Tabs at the bottom of the list with no number (or a higher number) will be kept active the longest, such as the tab you are currently viewing or tabs playing audio.
  • Host: Displays the website domain of the open tab.
  • Last Accessed: Shows the timestamp of the last time you clicked on or interacted with the tab. Older timestamps increase the likelihood of the tab being unloaded.
  • Base Weight and Secondary Weight: Internal metrics Firefox uses to calculate the importance of a tab. Tabs playing media, using webRTC, or running specific processes are given higher weights so they are not accidentally unloaded.
  • Memory: Shows the exact amount of RAM each tab is currently consuming.

If two tabs have the same Base Weight and Secondary Weight, Firefox will prioritize unloading the tab that is consuming more memory or the one that has gone the longest without being accessed.

Manually Unloading Tabs

While Firefox automatically unloads tabs only when system memory is critically low, you can force the browser to unload tabs manually using this page. You cannot choose a specific tab to unload from the list; instead, you trigger Firefox to unload them in the established priority order.

To manually unload a tab:

  1. Look at the top of the table to see which tab is currently listed at Priority 1.
  2. Locate the Unload button positioned above the top-right corner of the table.
  3. Click the Unload button.

Firefox will immediately discard the Priority 1 tab from your system's memory. The tab will remain visible on your tab bar, and its data will be cleared from your RAM. The list will then automatically update, moving the next tab in line up to the Priority 1 spot. You can click the Unload button repeatedly to continue putting tabs to sleep down the priority list. When you eventually click on an unloaded tab in your browser bar, Firefox will simply reload the webpage.