In addition to what Rich just wrote I just did a search. One of the solutions, the poster had accidently installed the wrong bit version of firefox. I believe that is not supposed to happen.
However, one way of telling is to navigate in your terminal to whereever firefox-bin is.
strings firefox-bin | grep lib64
# EXPECTED result for 64 bit /lib64/ld-linux-x86-64.so.2
You should have the 32 bit if you are on coreplus so I would expect you to see no result?
so I am guessing you could confirm with
strings firefox-bin | grep ld-linux-x86