As promised, details:
Just had a really Sad Path with my wife's Firefox install. It started with the 67.0.1 Trailhead release tonight and degenerated from there into a series of UX bloopers, each more cryptic and unfriendly than the last. I'm hoping this will get to some overarching Firefox Experience Manager who can untangle the things that went wrong and prioritize remediations for future users in this flow.
She was once-upon-a-time on Beta, though isn't now and I don't think has been for many months. Was on an old copy of 64 somehow, installed in her user dir, in ~/Applications. (macOS 10.13)
Firefox complained it was "critically out of date". It gave her a download link to a .dmg, at https://www.mozilla.org/en-US/firefox/new/?flowId=1e99919a-15ab-3444-865d-3bc950e7dd8e&fxVersion=64.0&isDefaultBrowser=1&searchEngine=google-2018&source=heartbeat&surveyversion=56&syncSetup=1&type=button&updateChannel=release&utm_campaign=YourFirefoxiscriticallyoutofdate.Anupdateisrequiredtostaysecure.&utm_medium=show-heartbeat&utm_source=firefox.
She dragged the downloaded FF 67.0.1 to /Applications (note: new location, not in her user dir), as prompted.
Firefox (Desktop) launched with "This installation of Firefox has a new profile" page (probably due to bug 1474285, which is an awful idea), meaning all her old stuff was (as far as she was concerned) suddenly gone. She had 2 copies of FF open at this point: old 64 and 67.0.1. The page threatened, with a twist of its mustache, "Enable Firefox Sync, or you'll never see your precious saved passwords again!" Cowed, she attempted to comply, beginning by doing so on Desktop.
It next demanded she use a second device (presumably to recover profile info from—something that made sense only to me, however) and thus demanded her phone number. She entered it. Got link on phone. Clicked. Turned out she already had FF on her phone, though rarely or never used, and so didn't have to install anything.
Firefox came up showing a support article welcoming her to iOS Firefox v67. (See attachment.)
That's a weird page. (I showed up to help about here.) I was expecting some handholding to show up on mobile at this point and help us finish setting up Sync. Instead there's this broken-looking headline on an irrelevant support article. In retrospect, I guess that's a | and not a capital I, but it makes a broken-looking headline in that font. A small detail in the scheme of this mess.
Anyway, there was no evident way to "sign in", as in the Desktop page's "Install Firefox on your smartphone and sign in to complete set-up". A screenshot of Mobile with the hamburger circled would have been great.
I didn't know offhand how to sign in myself (who ever signs in more than once?), so I decided to recover her profile the old-fashioned way.
I took over and tried to use Profile Manager to switch to her old profile, but it refused, claiming that the profile was actually newer than the current 67.0.1 version of FF (plainly wrong, right? bug 1556612?) and citing corruption concerns.
At this point, I went back to Mobile and finally found Sync signin under the hamburger menu (after looking under the ellipsis (Page Action, in retrospect) menu) and got her straightened out. (Having a menu whose semantic is "More" and another whose semantic would thus appear to be "More More" is disorienting.)
Teetered on the brink of her switching to Chrome, since it's recommended as "best practice" by her university's new Google Shared Drive training, which is what she was attempting to watch when all this went down. Apparently a lot of universities are using similar training. Expect an outflux of FF users as IT nudges clueless education users Chromeward.
Anyway, I hope we can smooth out some of these tangles for future hapless users. Cheers!