Let me see if I can translate this. Let me know if I got it right.
While using Firefox Search Engine
You mean you were using Firefox to search for something on the Internet using some search engine? If so, what engine (Google, Bing, Yahoo, etc).
something crashed my MBP 10:10:2 Yosemite
What does "crash" mean to you in that quote? Did you get error messages? Smoke? Screen indications? Fans running? What is a crash?
Turn off how? Power button for 10 seconds? Normal shutdown? What?
"Seized?" What symptoms? How long was it "seized?" Again, what symptoms? Fans running? Screen on/off/black? Mouse, trackpad working?
and when I finally got it back up
What did you do to get it "back up?"
my emails from yesterday 2016 were gone and I cannot find them.
Does "yesterday 2016" mean all mail from 2016 to yesterday? Or all emails from yesterday at about 8:16PM are missing (8:16PM is 2016 in 24 clock time).
Can you say exactly what you did for this rebuild? Any third party software involved?
and used Mail Prefs to delete some WiFi addresses
???? There is no access to WiFi addresses in Mail preferences at all, so what does that mean, please?
Assuming you meant "came unannounced" what does that mean? What came unannounced? If you meant "cane" what does that mean?
and still no lost emails.
Do you mean you don't have any lost now, or that none of the "lost" emails reappeared?
Any help would be welcome. Ron.
Happy to help, Ron, once we understand what is going on.