[CentOS] Firefox addons disabled - temporary fix

The currently available fix for Firefox doesn't work with ESR, but there's a temporary fix that works. At least, it's working for me:

Go to about:config and set xpinstall.signatures.required to false.

The Firefox folks say that a fix for ESR will be coming at some point, but at least this gets things working again in the short term.

It's not clear to me if the fixed ESR (when available) will require a new Firefox rpm to be created and installed or if it's something that will just show up by magic and start working or if any steps will have to be taken to enable it.