Well, write off hours wasted trying to coerce fresh Tor Browser to do exactly what I wanted with my precious seventeenth-circuit login cookies (as recovered from the browser console).  I finally gave up, and installed a persistent browser exclusively for Bitcointalk.org.  After checking the appropriate boxes and “only” trying three circuits to get a CAPTCHA, I am now allegedly logged in until the year 2023; oh yes, I backed up those cookies!

I thus hope to not be the canary in the CAPTCHA anymore; but I do care about this issue, and I will continue trying to adduce a workable solution.

Thanks to those who replied.  Now that I don’t face a steep login hassle, I will be catching up on this and other threads.