https://bugzilla.mozilla.org/show_bug.cgi?id=259356

20 indeed

I use this script with librewolf, give it a try, simply place it in $HOME/.local/bin name it librewolf and export that location as first in $PATH:

#!/bin/sh

APPHOME="$XDG_DATA_HOME/librewolf/HOME"
APPEXEC="$HOME/.local/opt/librewolf/librewolf" # Replace this with the path to librewolf

# XDG Check
if [ -z "$XDG_CACHE_HOME" ] || [ -z "$XDG_CONFIG_HOME" ] || [ -z "$XDG_DATA_HOME" ] || [ -z "$XDG_STATE_HOME" ]; then
	echo "One or more XDG Base dir variables not defined, bailing out"; exit 1
fi

# MAKE FAKEHOME AND LINKS
mkdir -p "$APPHOME/.local"
[ ! -e "$APPHOME/.local/share" ] && ln -s "$XDG_DATA_HOME" "$APPHOME/.local/share"
[ ! -e "$APPHOME/.local/state" ] && ln -s "$XDG_STATE_HOME" "$APPHOME/.local/state"
[ ! -e "$APPHOME/.config" ] && ln -s "$XDG_CONFIG_HOME" "$APPHOME/.config"
[ ! -e "$APPHOME/.cache" ] && ln -s "$XDG_CACHE_HOME" "$APPHOME/.cache"
[ ! -e "$APPHOME/.icons" ] && ln -s "$XDG_DATA_HOME/icons" "$APPHOME/.icons" # Some apps have hardcoded ~/.icons path

find "$APPHOME" -xtype l -delete
for FILES in $(find "$HOME" -maxdepth 1 -mindepth 1); do
	FILENAME=$(basename "$FILES")
	if [ ! -e "$APPHOME/$FILENAME" ]; then # LINK IF IT DOESN'T EXIST
		ln -s "$FILES" "$APPHOME/$FILENAME"
	fi
done

# START APP AT APPHOME
HOME="$APPHOME" "$APPEXEC" "$@" || notify-send "App not found"