Tab Unloading is a new feature that helps reduce memory usage by unloading tabs that you are not actively using. To avoid crashes, Firefox will automatically select and unload these open tabs when the system's memory is low, starting in Firefox version 93 on Windows. This is a smart process that avoids unloading tabs that are playing media, using Picture-in-Picture, or WebRTC. For more technical information, see this blog post.
The about:unloads page is built into Firefox 94 on all Desktop platforms. It displays information about your open tabs, such as the order of priority for unloading tabs, the last time you accessed each tab and the memory each tab is consuming. To open this page, type about:unloads in the address bar and press EnterReturn.
You can manually unload your least-recently-used tabs by going to the about:unloads page and clicking on thebutton that appears above the table, on the right.