'''Background''' I have recently made a [https://support.mozilla.org/en-US/questions/1271362 modification] to my Firefox profile folder to allow the New Tab page to have a background image, but now I am noticing some strange behavior. When first running Firefox it looks like [https://i.stack.imgur.com/8L5DB.png this]. As you can see, for the sites that don't have a high-quality favicon available, Firefox uses a letter and the low-quality favicon. What I'm pointing out here is that the background for these is transparent. However, when I open some sites and navigate around, I come back to see [https://i.stack.imgur.com/MhSdm.png this]. There is now no visible letter and the background color for these icons have changed to white. I cannot seem to reproduce this, it just eventually happens after regular use. This can be fixed by closing the browser and reopening it, but obviously, that's an inconvenience. '''Question''' Is there a way I can force the icon backgrounds to be transparent, or at least change the solid color to something more fitting to the theme? If possible, please let me know if there is a reason this is happening. ''Note: I would rather not resort to setting a custom thumbnail for each of these because I like the way Firefox handles it by default. I'm just looking to fix the "ugly" white background that comes out of nowhere.''