A new mark
The name is now a drawing rather than six characters of monospace: a T and a p sharing one stem. The same pair, on its own, is the icon — so the tab, the bookmark, the phone home screen and the Android launcher all get a real icon instead of a letter the browser guessed at.
The old mark was T>pipe set in whatever monospace the machine had, with the caret borrowed from a shell prompt. It cost nothing and looked like what it was: a typeface the browser happened to own, which meant the name was a slightly different shape on every screen it appeared on.
What the mark is
A capital T and a lower-case p fused along the stem they share, with the rest of the word — ipe — beside them. The T is the colour of the text around it and the p is cyan. Because it is drawn rather than set, it is the same shape at any size, on any machine, and in a screenshot somebody takes of it.
It is inline SVG in the page rather than an image file, for the two things an image cannot do: take the colour of the text it sits next to, and arrive in the same breath as the markup instead of a request later, which is what leaves a hole in the corner a visitor looks at first.
Where it appears
The two fused letters alone, on a dark rounded square, are the icon. At sixteen pixels a whole word is a smudge; two overlapping letters are still two letters.
One drawing produces all of it. The browser tab and the bookmark take the SVG; an iPhone home screen and an Android launcher take PNGs, the Android one drawn smaller inside its square so a launcher can crop it without cutting the letters; favicon.ico exists for the things that ask for it without reading the page first — a link unfurl, a feed reader, a connector list. The browser extension uses the same icon in the toolbar and on its Web Store listing, and an assistant adding the connector is handed the same file.
Nothing else changed: no colours on the site moved, and no page was redrawn around it.
Related: saving a web page as Markdown, and what to look for in an online document converter.