From that point onwards, I'd just search on userstyles.org. In the advanced search, select "App" from the first dropdown, then it'll show you pretty much only Firefox-styles.
If you found something that suites your taste, you can click the "Show CSS"-link and copy-paste that into userChrome.css. Just make sure that you don't have the @namespace-line twice.
As for the CSS-file, you have to create a folder called "chrome" in your profile folder and then in that folder create a file "userChrome.css".
In that file, you have to have the following line at the top of everything else: "@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xu...
From that point onwards, I'd just search on userstyles.org. In the advanced search, select "App" from the first dropdown, then it'll show you pretty much only Firefox-styles.
If you found something that suites your taste, you can click the "Show CSS"-link and copy-paste that into userChrome.css. Just make sure that you don't have the @namespace-line twice.
This for example sets the minimal tab-width rather low: https://userstyles.org/styles/53019/firefox-5-minimal-browse...
You can also find userstyles that for example hide the close-button until you hover over the tab or merge the close-button with the favicon.