You can add a custom background image beneath the Firefox Color pattern with the following userChrome.css (wallpaper.jpg located in the same folder):

#navigator-toolbox::before {
  background: url("wallpaper.jpg") !important;
  width: 100%;
  height: 100%;
  position: absolute;
  z-index: -1;
  content: "";
}

html[sizemode="normal"] #navigator-toolbox::before {
  border-radius: 10px;
}

#navigator-toolbox {
  background-color: unset !important;
}

Could you explain how to get to the userchrome.css file and also how would I align the custom image toward the top of the image and fixed to the right corner like I can in Firefox Color?

Nevermind, thank you so much. I got it fully working perfectly with your code and a little tweaking help with ChatGPT. Here is the exact code that worked for me to place an image in the top right corner with no repeat and have a fully functioning toolbar:

#navigator-toolbox::before {
  background: url("wallpaper.jpg") no-repeat top right fixed !important;
  width: 300px !important; /* Set the width to 100 pixels */
  height: 95px !important; /* Set the height to 100 pixels */
  position: fixed !important;
  top: 0 !important;
  right: 0 !important;
  z-index: 0 !important;
  content: "";
}

#navigator-toolbox {
  background-color: #943022 !important;
  z-index: 10 !important;

}

NOTE: the 1's in front of the navigator-toolbox are actually hashtags # Thanks so much man much appreciated.