Ironically, it was copying google's chrome LAF that led to the decline in firefox since v57. They had to kill XUL to be able to keep up with the Chrome UI chan

Ironically, it was copying google's chrome LAF that led to the decline in firefox since v57. They had to kill XUL to be able to keep up with the Chrome UI changes, and at that point killed off a vast amount of plugins, leaving firefox with no real advantage over chrome, but all the speed disadvantages compared to chrome.