PPA install is broken

[zoomosis]

Attempting to use "sudo deb-get install firefox-esr", the PPA's repo is added but the package is never installed.

I think the logic in install_ppa() is broken:

if ! dpkg -l "${APP}" >/dev/null 2>&1; then
     eula
     apt-get -q -y install "${APP}"

Here "dpkg -l" will return non-zero if a package is missing, but the if statement is checking for zero.

Even if this worked there's still the issue of "dpkg -l" returning zero for packages with only config-files installed. So if you had firefox-esr installed previously then uninstalled it with "apt remove", "deb-get install" won't reinstall it.

Rather than "dpkg -l" I suspect it would be more reliable to parse the output of "dpkg-query -s firefox-esr" and not rely on the return code at all.