steps to reproduce:
1. open a blank tab
2. add a shortcut
3. use the following values:
Title: testing
URL: https://www.userchrome.org/
4. click "Use a custom image..." and provide the following URL:
https://www.userchrome.org/img/Fxcss_256.png
5. click the preview button
6. notice that the icon appears normally with a caption of "testing"
7. click "add"
8. notice that a new placeholder for the website labeled as "testing" appears but the icon is missing
expected results:
1. a new icon for a website named "testing" should appear along with the expected icon picture
observed results:
1. a new icon for a website named "testing" appears but the icon picture is missing (grayed out)
older related issue:
https://support.mozilla.org/en-US/questions/1231726
