We have now approached the problem again by refining our low-memory detection and tab selection algorithm and narrowing the action to the case where we are sure we’re providing a user benefit: if the browser is about to crash. We have experimented with tab unloading on Windows in the past, but a problem we could not get past was that finding a balance between decreasing the browser’s memory usage and annoying the user because there’s a slight delay as the tab gets reloaded, is a rather difficult exercise, and we never got satisfactory results. Firefox is now better at surviving these situations. And of course, there are the tab hoarders, (no judgement here). Or perhaps those users simply trying to play a memory-intensive game or using a website that goes a little crazy. We believe this may especially benefit people who are doing heavy browsing work with many tabs on resource-constrained machines. Unloading tabs allows Firefox to save memory leading to fewer crashes and avoids the associated interruption in using the browser. On Windows, out-of-memory (OOM) situations are responsible for a significant number of the browser and content process crashes reported by our users.

The tab’s scroll position and form data are restored just like when the browser is restarted with the restore previous windows browser option. When a tab is unloaded, the tab remains in the tab bar and will be automatically reloaded when it is next selected.

This feature is currently enabled on Windows and will be deployed later for macOS and Linux as well. Starting with Firefox 93, Firefox will monitor available system memory and, should it ever become so critically low that a crash is imminent, Firefox will respond by unloading memory-heavy but not actively used tabs.

Firefox 45.0 crashes when closing tabs