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Sleep Mode is a new browser extension for the Firefox web browser that hibernates all but the active tab on activation. Doing so frees up memory, saves battery, and may speed up operations.

Web browser users who open multiple tabs during browsing sessions may notice that memory use increases when doing so. Depending on the available resources, especially memory and battery, thresholds may be reached that may slow down operations.

Third-party tools and browser extensions may help tame memory usage of browsers automatically, semi-automatically or manually. Firefox lost a good chunk of extensions designed to improve memory usage as they relied on the old extensions system.

Firefox 67 may unload tabs automatically in low memory situations similarly to how Google Chrome does it since 2015.

Sleep Mode

Sleep Mode is a simple extension that is highly beneficial in some cases. The extension adds an icon to the main Firefox toolbar during installation that you may interact with.

The icon acts as a toggle. A click starts sleep mode functionality. Any tab, with the exception of the active tab and tabs that have not loaded fully or not at all, are put into Sleep Mode to free up memory and improve power usage and performance of the system.

Sleep Mode unloads the site and adds Sleep Mode to the beginning of the page title; the latter may hide the entire page title which makes identification of the unloaded site difficult.

A quick test with just a few open tabs reduced memory usage by over 200 Megabytes (from 600 to 400).