Restore the preference the tab close buttons.
In Firefox, you could change the appearance of the tab close button. Unfortunately, in Firefox 31, that feature has been removed.
This addon will restore the feature.
You can change the tab close button appearance by setting the value below in
0. Display a close button on the active tab only. (Same behavior of Firefox 31 and later)
1. Display close button on all tabs. (Default of Firefox 30 and earlier)
2. Don't display any close buttons.
3. Display a Tabstrip close button.