Er… Are you quite sure the image file names you’ve been trying were identical? No errors?
All works as expected here using both .svg and .png image files. :)
E.g. in your post above your profile chrome folder image file is named ‘fb1.png’… whilst your image file name in your userContent.css code is ‘fb1.svg’. Yes, the image file names match… but No, the file type suffixes do not match!
Tested here using a .svg image file and a new profile of Fx125.0.2 on Win10… with just the rule code copied directly from your post (above)… adding a Firefox logo .svg image file downloaded from here… placed in profile ‘chrome’ folder… then renamed ‘fb1.svg’ as per your example:
Er… Are you quite sure the image file names you’ve been trying were identical? No errors?
All works as expected here using both .svg and .png image files. :)
E.g. in your post above your profile chrome folder image file is named ‘fb1.png’… whilst your image file name in your userContent.css code is ‘fb1.svg’. Yes, the image file names match… but No, the file type suffixes do not match!
Tested here using a .svg image file and a new profile of Fx125.0.2 on Win10… with just the rule code copied directly from your post (above)… adding a Firefox logo .svg image file downloaded from here… placed in profile ‘chrome’ folder… then renamed ‘fb1.svg’ as per your example: