Because:
- A user who reaches the pairing flow on a computer that is not running
Firefox has no way forward — the pairing hand-off is browser-to-browser —
so they need to be told to open Firefox and given a way to install it.
- Adds the desktop screen prompting the user to install Firefox.
This commit:
- Adds `packages/fxa-settings/src/pages/Pair2/Authority/DownloadFirefox/index.tsx`,
a presentational card rendering the heading, the instruction pointing at
firefox.com/pair, the desktop/mobile sync illustration, and a full-width
"Download Firefox" call to action. It takes no props: the CTA is an external
link, so it is wired here rather than left to the route.
- Follows the desktop element order from Figma — heading, subcopy,
illustration, CTA — which is the reverse of the Pair2 mobile cards, and
omits the in-card Firefox lockup that the mobile cards carry.
- Points the CTA at the existing `LINK.FX_DESKTOP` constant, the same
destination `Pair/Unsupported` hardcodes today, and styles it with
`cta-primary cta-xl` inside a flex wrapper so the link stretches the way a
primary button does. `FtlMsg` sits inside `LinkExternal` so translating the
label does not clobber the component's "Opens in new window" screen-reader
text.
- Reuses `AppLayout`'s card surface, which already matches the Figma frame
exactly: 480px wide, 32px horizontal and 36px vertical padding.
- Adds `en.ftl` with the three new strings, `index.stories.tsx`, and tests
covering the copy, the illustration's accessible name, the CTA's href, and
drift between the component's fallback text and the Fluent bundle.
Closes #FXA-14239