Tab Warming, currently not enabled by default in Firefox Nightly, when turned on, loads tab contents in the background when you mouse over a tab (assuming you’ll switch to it), when you click on that tab, eventually, page content will be displayed in the browser.
For most sites, you won’t notice significant difference, but, for certain sites like this you’ll feel tab switching is faster in Firefox.
UPDATE: Mozilla is currently planning to ship the tab warming feature to Firefox Windows and Linux users with Firefox version 61.
Tab Warming in Firefox
You can enable tab warming in Nightly by flipping the below preference in about:config
Mozilla’s Milke Colney, who works on Electrolysis says ” Tab warming is ‘is what we’re calling the process of pre-emptively rendering the layers for a tab, and pre-emptively uploading them to the compositor, when we’re pretty sure you’re likely to switch to that tab”.