How to Enable Skeleton UI in Firefox

You can enable the new Skeleton UI in Mozilla Firefox Nightly. It works like an app startup indicator by showing a UI placeholder to notify you that Firefox is starting.

The new placeholder is called skeleton UI. It solves the browser slow start issue.

When you just started Windows and click on the Firefox icon, the browser runs for the first time performing “cold start”. It takes longer than the second start, and the user doesn’t see any visual indication.

The lead developer Doug Thayer, a Firefox Platform Engineer, said that it may take up to 19 seconds before users see an indication that Firefox is loading.

By adding the new skeleton UI feature Firefox will give users a visual indication of the browser loading as much as 15 seconds faster than now.

The new skeleton UI feature is just a blank window that appears in 3 seconds after the user clicked on the Firefox icon. If you want to try it, install Nightly and change browser.startup.preXulSkeletonUI to true.

Enable Skeleton UI in Firefox

1. Type about:config in the address bar.
2. Click on Accept the risk and continue.
3. Type browser.startup.preXulSkeletonUI in the search area.
4. Set the preference to true to enable the skeleton UI.
5. A value data of false will disable it.
6. Relaunch Firefox.

You should now notice a faster user interface when start Firefox for the first time.

This is a feature which allows us to create the first window and populate it with a non-interactive placeholder before we load xul.dll. On some systems, this can mean we can give visual indication of Firefox launching as much as 15 seconds sooner than normal (loading xul.dll can take a while).

Said the developer.

The current startup delay values noted are

• 19 seconds before visual indication of Firefox launch
• after that, you see a blank window
• 3 seconds before the window frame to appear
• 8 seconds before you get about:home open.

With a new feature, the 19 second delay has been reduced by 9 seconds.

In addition to skeleton UI, Mozilla is adding a new Proton design to the browser,

That’s all.

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