How to hide the Add Bookmark button from Firefox's URL bar

If you use an external Bookmarks manager (such as Linkwarden or Raindrop.io), you may want to hide the default Add Bookmark button (the Star) from your URL bar.

First, create a userChrome.css file.

Then, add the following somewhere underneath the @namespace line:

#star-button-box {
	width: 0.1px !important;
	overflow: hidden !important;
	padding-inline: 0 !important;
}

Other sources suggest setting display: none, or visibility: collapse, but these also hide the Add Bookmark dialog box (e.g. what comes up when you press Ctrl+D), which then causes bookmarks to be added immediately, which defeats the point. The above solution retains the ability to cancel creating the bookmark accidentally, as of Firefox 132.

I learned this information from this Reddit comment.