Firefox Nightly uses a new skeleton UI on start on Windows

[harlan4096]

If you are using Firefox Nightly on Windows 10, you may have noticed a new more-or-less blank user interface that gets loaded on the very first start of the browser. Mozilla calls it a skeleton UI, and it is designed to give users early feedback that Firefox is indeed starting up.

The bug report on Mozilla's Bugzilla website highlights that Firefox's startup is very slow on some systems. According to the lead developer, Firefox would take 19 seconds on a reference system before it gave any indication that it was launched.

A blank window is displayed at that point, then, after three seconds the browser chrome, and after another eight seconds the homepage. Consecutive starts are faster on the system, but the cold start of the browser is quite slow.How long it takes depends on the system's resources and performance, but long periods without visual indicator are a problem.

Mozilla decided to create a skeleton UI for Firefox that acts as an early visual indicator that the browser is indeed starting.

The enabling of the skeleton UI in Firefox Nightly reduces the time it takes to show any sign of a launch significantly, especially on low performance systems.
 

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).

Mozilla hopes that "it will improve the overall snappiness of startup even on fast systems".

The feature landed in Firefox Nightly but only for Firefox running on Windows 10 devices. It is likely that Mozilla will introduce the change to other systems Firefox is compatible with, but for now, it is Windows 10 only.

Firefox users who prefer not to see the skeleton UI on start, e.g. because it is causing issues on the system or because you dislike the switching of the blank window to the full browser UI, can disable it in the browser's advanced preferences.

Here is how that is done:

1. Load about:config in the Firefox address bar.
   
2. Confirm that you will be careful.
   
3. Search for browser.startup.preXulSkeletonUI.
   
4. Set the preference to TRUE to enable the Skeleton UI, or to FALSE to disable it.
   
5. Restart the Firefox web browser.
   

If you set it to FALSE, you will notice that Firefox won't use the skeleton UI anymore on the system. You may restore the feature at any time by setting it to TRUE.

Now You: Have you noticed the new skeleton UI? What is your take on the feature?
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