On x86_64, most plugins don't work. I tried the wrapper thing and could not watch flash.
Don't want to remove firefox.x86_64, even though that's what most people seem to do. Then they just run firefox.i386. Don't want to do that because that requires the removal of the 64 bit apps like yelp and devhelp that depend on firefox.
But it is possible to stop firefox-64 bit from running
Solution: edit the /usr/bin/firefox script and comment out the 64 bit lines, like so:
#if [ -x "/usr/lib64/firefox-188.8.131.52/firefox-bin" ]
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