When Firefox is already running and XRemote is used to open the new URL, a URL
with a comma (,) will be passed to Firefox incorrectly. This is due to the
XRemote command parsing. The solution is probably to encode commas into the
relevant URL entities; same goes for spaces, which can also be mangled by XRemote.

My solution:
if [ "${USE_EXIST}" -eq "1" ] && [ "${ALREADY_RUNNING}" -eq "1" ]; then
  opt=`echo -n "$opt" | sed -e 's/,/%2c/g' -e 's/ /%20/g'`