I decide to post this blog, after long search forum with obselete code to instal Firefox and thunderbird on Raspbery pi 3B+. Last tested on March 22, 2021.
What I did is to make a clone of the repositor on Xubunut 18, import the repository key and install the packages
enjoy
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#Add repository (cloned from xubuntu 18)
sFilename=ubuntu-bionic-security.list
echo "
deb http://ports.ubuntu.com/ bionic-security main restricted universe multiverse
deb-src http://ports.ubuntu.com/ bionic-security main restricted universe multiverse" | sudo tee /etc/apt/sources.list.d/$sFilename
sudo chmod 644 /etc/apt/sources.list.d/$sFilename
#Import key
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3B4FE6ACC0B21F32
#Install package
sudo apt update
sudo apt -y install firefox thunderbird
sFilename=ubuntu-bionic-security.list
echo "
deb http://ports.ubuntu.com/ bionic-security main restricted universe multiverse
deb-src http://ports.ubuntu.com/ bionic-security main restricted universe multiverse" | sudo tee /etc/apt/sources.list.d/$sFilename
sudo chmod 644 /etc/apt/sources.list.d/$sFilename
#Import key
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3B4FE6ACC0B21F32
#Install package
sudo apt update
sudo apt -y install firefox thunderbird
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