Was the Customize option not working to move it?

The syntax was giving me a bunch of errors everywhere so it wouldn't take. It just didn't do anything. Sorry, I'm not really a coder I'm not sure why it wasn't working per-se, just that it didn't. Maybe the code just needs to be updated? I saw that people recommended chrome user files, and the stylish extension to do it, but I couldn't get it to work. Maybe I did something wrong?

I solved it! I used this video:

https://www.userchrome.org/how-create-userchrome-css.html

And this code:

.tabbrowser-tab .tab-throbber, .tabbrowser-tab .tab-icon-image, .tabbrowser-tab .tab-sharing-icon-overlay, .tabbrowser-tab .tab-icon-overlay, .tabbrowser-tab .tab-label-container, .tabbrowser-tab .tab-icon-sound {

 -moz-box-ordinal-group: 2 !important;

} .tabbrowser-tab .tab-close-button {

 margin-left: -2px !important;
 margin-right: 2px !important;

}

And it works perfectly!!

Note that this code that moves the close button to the left would be a lot easier:

.tabbrowser-tab .tab-close-button {-moz-box-ordinal-group: 0 !important;}