Thanks for adding the ability to change the icon color scheme! :D

For those who want to make the icon stay at the very end of the URL bar, put this in your userChrome.css (google it if you don't know what that is):
#_e1ed7a80-7c11-4f7e-968b-79b551a0067f_-page-action {
-moz-box-ordinal-group: 2 !important;
}

UPDATE: For those on FF58, try this CSS:
.urlbar-icon.urlbar-page-action[aria-label="Reload page"],
.urlbar-icon.urlbar-page-action[aria-label="Stop"]{
-moz-box-ordinal-group: 99 !important;
}