html5debug: command not found

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/html5debug - from package: libhtml-html5-parser-perl

You may install the required package with command apt-get install {package}

Error in other languages:
html5debug: bevel nie gevind nie
html5debug: comandă negăsită
html5debug: comando não encontrado
html5debug: commande introuvable
html5debug: command not found
html5debug: käsku ei ole
html5debug: không tìm thấy lệnh
html5debug: komanda nerasta
html5debug: Kommando nicht gefunden.
html5debug: kommandot finns inte
html5debug: komut yok
html5debug: nie znaleziono polecenia
html5debug: níor aimsíodh an t-ordú
html5debug: no se encontró la orden
html5debug: no s'ha trobat l'ordre
html5debug: opdracht niet gevonden
html5debug: parancs nem található
html5debug: perintah tidak ditemukan
html5debug: príkaz nenájdený
html5debug: příkaz nenalezen
html5debug: команда не найдена
html5debug: командата не е открита
html5debug: 命令找不到
html5debug: コマンドが見つかりません