nspr-config: 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 CentOS possible default full paths are:

/usr/bin/nspr-config - from package: nspr-devel

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/nspr-config - from package: libnspr4-dev
/usr/lib/icedove-devel/sdk/bin/nspr-config - from package: icedove-dev
/usr/lib/iceweasel-devel-38/sdk/bin/nspr-config - from package: iceweasel-dev

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