Firefox Tab Warming explained

Tab Warming is a relatively new feature of the Firefox web browser that can best be described as preloading when switching tabs. Mozilla’s intention with the feature is to speed up the tab switching process by improvement the performance of the switching process.

While Firefox does a very good job most of the time when it comes to the tab switching performance, some sites have noticeable delays between activing the tab and Firefox switching to it.

A page that uses SVGs and CSS for animation may have a noticeable tab switching delay. Tab Warming works by initiating the rendering of the page the moment the mouse cursor hovers over a background tab in the Firefox browser.

Firefox gains the time that it takes the user to activate the tab with a mouse-click to start the rendering early.

With tab warming enabled, when you hover over the tab with your mouse cursor, the rendering of that sophisticated SVG will occur while your finger is still on its way to click on the mouse button to actually choose the tab.

Here are all scenarios played out for you:

	Tab Switching enabled	Tab Switching disabled
hover and click	delays are reduced or eliminated	may notice delays on select pages
hover and no click	minimal resource usage	no change

Tab Warming eliminates the noticeable delay that Firefox users would experience without the feature completely in best case. It will reduce the delay at the very least if delays were noticeable on a web page. Worst case is that users hover over tabs but don’t activate them.

Tab Warming is not enabled right now in the web browser. Firefox Nightly supports Tab Warming already but users need to enable the feature before it becomes active.

1. Load about:config?filter=browser.tabs.remote.warmup.enabled in the web browser’s address bar.
2. Double-click on the preference.

A value of True means that Tab Warming is enabled, a value of False that it is disabled.

A quick test confirms that Tab Warming makes a difference. You may not notice a difference on all tabs open in the browser; if a tab switch was instant, Tab Warming cannot speed that up further. Your mileage may vary as things may depend on the device as well.

I did not notice a performance impact after enabling Tab Warming in Firefox Nightly.

Closing Words

Tab Warming is a useful feature that promises to improve the tab switching delay in the Firefox browser.

Now You: What’s your take on Tab Warming? Did you try it?