Add the first FxA Nimbus A/B test. Test 8 value proposition headings against
the current control on the desktop QR promo in the authentication flow, and
ship the updated promo design that makes room for the longer strings.
Declare the promo-qr-mobile feature in the FML with two variables, enabled
and branch. A single branch slug drives the heading and the QR code
together, because each QR scans to its own Bitly link and a mismatched pair
would misattribute the download. Every channel defaults to the control, so a
Cirrus failure is a no-op, and an unknown slug falls back to the control, so
a typo in Experimenter cannot break the promo.
Declare all 9 headings as literal FTL ids so the l10n extraction finds them,
and pick one at runtime with useFtlMsgResolver. The CTA moves below the QR
and changes wording, so it takes a new -v2 id and translators re-translate
rather than keep the old string.
Rebuild the component to the updated design. The logo above the heading is
gone, because the Bitly QR already embeds the Firefox glyph in its centre.
The 230KB qr-mobile-kit.svg gives way to real fox vectors and a per-branch
QR, about a 10x reduction. The heading used text-md, which is not in the
font scale and so set no size at all; it is now text-sm font-bold.
Report branch and nimbus_user_id on promo_qr_mobile.view. Cirrus reports
enrollment itself, so the app must stamp nimbus_user_id on its own events
for the analysis to join them. A CMS-supplied image carries no branch, so
those users get the control copy and report no branch. The render waits on
Nimbus so the control does not paint and then swap.