mozplugger-helper: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/mozplugger-helper - from package: mozplugger

You may install the required package with command apt-get install {package}
Error in other languages:
mozplugger-helper: bevel nie gevind nie
mozplugger-helper: comandă negăsită
mozplugger-helper: comando não encontrado
mozplugger-helper: commande introuvable
mozplugger-helper: command not found
mozplugger-helper: käsku ei ole
mozplugger-helper: không tìm thấy lệnh
mozplugger-helper: komanda nerasta
mozplugger-helper: Kommando nicht gefunden.
mozplugger-helper: kommandot finns inte
mozplugger-helper: komut yok
mozplugger-helper: nie znaleziono polecenia
mozplugger-helper: níor aimsíodh an t-ordú
mozplugger-helper: no se encontró la orden
mozplugger-helper: no s'ha trobat l'ordre
mozplugger-helper: opdracht niet gevonden
mozplugger-helper: parancs nem található
mozplugger-helper: perintah tidak ditemukan
mozplugger-helper: príkaz nenájdený
mozplugger-helper: příkaz nenalezen
mozplugger-helper: команда не найдена
mozplugger-helper: командата не е открита
mozplugger-helper: 命令找不到
mozplugger-helper: コマンドが見つかりません