User Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:73.0) Gecko/20100101 Firefox/73.0

Steps to reproduce:

1. Set the Firefox theme to light or default (the about:blank page should be white).
2. Install the 'Group Speed Dial' extension which creates a new tab page (a moz-extension URL) with a black background. If the new tab page is not black, change it in the extensions Options page.
3. Create a bookmark to a web page that has a dark background ( https://jasonfarrell.com/misc/deadpixeltest.php?p=1 ).
4. Create a new black tab (Ctrl+T).
5. Click on the new bookmark that has a black background, loading the bookmark in the same page as the new tab.

Actual results:

On step #5, the page immediately turns white when the bookmark is clicked. If the next page loads quickly, this may look like a white flash. If the transition is slower, the page will stay white for a longer period of time until the next page is shown. The white flash also appears when using the forward/back buttons to switch between the two pages. Note that the change in color is also very noticeable when having a dark about:blank page and switching from a moz-extension page to an http page with light backgrounds.

Expected results:

When loading one http URL after another on the same page, there is a seamless transition from one background color to the next. There is no color change during the transition. Even with extensions that change a pages background color like 'Dark Reader', the change is still seamless. It would be nice if tabs with moz-extension URLs behaved in the same manner, not loading the about:blank page color, when switching to http URLs.

Hi,

Thank you for submitting this report. It seems our developers are currently working on this issue. Thus I am marking this as a duplicate of bug 1408122.

Take care.