Shawn,
Sorry for the issues. You should be fixed up now. I honestly don't know what was going wrong, but I just manually created the initial DB tables for JFBConnect. Then, I installed the extension like normal and it automatically upgraded the tables like it should. So, it can write to the database and do what it needs to, but something was preventing it from doing the initial install of tables.
Either way, 4.3 shouldn't have broken things that much.. so something was wrong there. The 5.0 releases have a check to make sure you're installing in the proper Joomla version though, so this definitely shouldn't happen going forward to you or anyone else.
Please test and let us know if you run into any other issues. Things looked good to me though.
Thanks,
Alex