display in Firefox in a 900px-wide window
GettingStarted's task toolbar can overflow and look weird if your window isn't wide enough. See attached screenshot, note buttons and close boxes appearing outside the dark background. It happened to me half-HD screen window (960px wide), but that's because I zoom fonts; At 100% the overflow happens at around 905px in Firefox.
The appearance glitches are similar in Chrome.
Changing mw-gettingstarted-toolbar to "display: table" greatly improves the appearance at narrow widths in Firefox but causes other problems in Chromium.