xfbrowser4: 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

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 CentOS possible default full paths are:

/usr/bin/xfbrowser4 - from package: xfce-utils

You may install the required package with command yum install {package}
Error in other languages:
xfbrowser4: bevel nie gevind nie
xfbrowser4: comandă negăsită
xfbrowser4: comando não encontrado
xfbrowser4: commande introuvable
xfbrowser4: command not found
xfbrowser4: käsku ei ole
xfbrowser4: không tìm thấy lệnh
xfbrowser4: komanda nerasta
xfbrowser4: Kommando nicht gefunden.
xfbrowser4: kommandot finns inte
xfbrowser4: komut yok
xfbrowser4: nie znaleziono polecenia
xfbrowser4: níor aimsíodh an t-ordú
xfbrowser4: no se encontró la orden
xfbrowser4: no s'ha trobat l'ordre
xfbrowser4: opdracht niet gevonden
xfbrowser4: parancs nem található
xfbrowser4: perintah tidak ditemukan
xfbrowser4: príkaz nenájdený
xfbrowser4: příkaz nenalezen
xfbrowser4: команда не найдена
xfbrowser4: командата не е открита
xfbrowser4: 命令找不到
xfbrowser4: コマンドが見つかりません