I put quite a lot of work into getting st and ct (optional) ligatures into the Linux Libertine typeface. And, turned them on by default in my copy.

And, I have my browser set to use Linux Libertine for all text, whether "serif", "sans", or whatever the page server said it ought to be. (Button wingdings something look odd.)

So, I don't see anything odd on the page, but I do see "st" ligatures. Just not theirs.

On my phone, where even Firefox utterly refuses to use the fonts it is directed to, I see ligatures in the sans-serif font, which is just ugly. But they do not make the sans-serif any worse than it always is.

I read your comment and thought "STar Wars does it, what's the issue?" And then I opened tfa... The ligature doesn't even make sense.

PS: For those who don't see it, the ligature is a circumflex connecting the top of the t with a serif coming out the top end of the s, which is even weirder because it's a sans serif font.

I don't see any in Chrome on a Mac. Is it a font issue?

Where are you seeing them? As far as I can tell the CSS styles tell the browser to use the system fonts.