Firefox tab close button on all tabs

Visibility of tab's close button can be set by modifying browser.tabs.closeButtons through about:config. The values are:

// Where to show tab close buttons:
// 0  on active tab only
// 1  on all tabs until tabClipWidth is reached, then active tab only
// 2  no close buttons at all
// 3  at the end of the tabstrip

The problem is, that when browser.tabs.closeButtons is set to 1 the close button visibility depends on the opened tab number. If there are more tabs than the tabbar can show it goes into overflow mode and thus the tab close buttons are gone. This can be fixed by adding a few lines to your userChrome.css:

.tab-close-button { display: -moz-box !important; }
.tabbrowser-tab[pinned] .tab-close-button { display: none !important; } /* hide close buttons on app (pinned) tabs */