about:preferences Change Block List contains an occurrence of "Firefox"

This is a spinoff from legacy/trac#27905 (moved). There is an occurrence of Firefox within the about:preferences Change Block List "dialog" which was fixed in Firefox 61 to pull the product name from brandShortName. Since it will not be easy to backport the fix to ESR60, we will pick this up with ESR68 (see ​https://hg.mozilla.org/mozilla-central/rev/8ebf84e9825d).