Note that FoxyProxy plugin is incompatible with the firefox-esr package in Kali rolling now. Requires to use FoxyProxy v3.6.5. Replacing code therefore with:
#--- FoxyProxy Basic echo -n '[4/11]'; timeout 300 curl --progress -k -L -f "https://addons.mozilla.org/firefox/downloads/file/579775/foxyproxy_basic-3.6.5-fx+sm+tb.xpi?src=version-history" \ -o "${ffpath}/foxyproxy-basic@eric.h.jung.xpi" \ || echo -e ' '${RED}'[!]'${RESET}" Issue downloading 'FoxyProxy Basic'" 1>&2