fix(firefox): do not split longopt argument

In the current implementation, an argument --longopt='-MOZ_LOG=xxx'
would be doubly split.  We avoid splitting the option argument of a
long option '--longopt=...'.

Author: akinomyoga

completions/firefox

@@ -5,7 +5,7 @@ _comp_cmd_firefox()
     local cur prev words cword was_split comp_args
     _comp_initialize -s -- "$@" || return
 
-    [[ $cur == -MOZ_LOG*=* ]] && prev=${cur%%=*} cur=${cur#*=}
+    [[ ! $was_split && $cur == -MOZ_LOG*=* ]] && prev=${cur%%=*} cur=${cur#*=}
 
     case $prev in
         --help | --version | --display | --UILocale | -MOZ_LOG | --new-window | --new-tab | \