I had the same challenge with Netfirms and just now I found a way to solve it. I simply changed my PHP version to 5 using my Netfirms cPanel (PHP section) and it works. I couldn't login with any username and password (including Admin!) and there was a MySQL coonection error. Now I can simply login. But I am just trying to check other probable problems.
P.S: The problem still exists but it randomly appears. I have trouble loging in with any username and password entered I got this error:
Lost connection to MySQL server during query
Installing and upgrading help
Installation holds at "setting up module tables" page
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