No, I don't.
Even if it is one percent (which I highly doubt) and that one percent is committed enough then that's enough of a core to guarantee the success of the project. It doesn't need a team of 1000 to build a browser, much less to keep an existing one patched and rolling along.
A non-Chromium browser needs to maintain a critical mass of users to be sufficiently large to ensure that the world wants to stay compatible with it, and having 1% of marketshare is not sufficient for that, no matter how committed these users are - if firefox drops to 1%, then it becomes irrelevant and the project has failed at its goals as the "web standards" become equivalent to whatever chromium does.
Browsers get influence to keep the web as we want it to be mostly based on the quantity of browser users which websites want to attract and keep; without that all the best code in the world is useless and doesn't even give you a seat at the table, much less a strong say for how the de-facto standard web practices will change.
As a browser maker your "concerns" should really be web/internet standards. If websites and webapp builders aren't complying with standards and are building their stuff to only work in non-standard compliant browsers that's a separate problem that no web browser can solve.
You should do that math again.
>And I suspect that the FF users of old care very much
But do they? Firefox's rise was largely due to IE6 being pure trash, and the average user of a web browser in 2008 being a lot more knowledgeable than the average user today.
Marketshare, by definition, is the share of the market. The market has expanded dramatically, but desktop browsing itself has plummeted, and a lot of users are just going to default to whatever they're using on their primary device (their phone), which is Google. "Google" is synonomous with using the internet in the same way that the internet explorer logo used to be in the mid 2000s.