Created a little Bash script on Github that reads your locally installed Firefox and Thunderbird versions and compares them to the newest versions available for download.
You can use it if:
- you manually installed Firefox and Thunderbird with root privileges
- you are an unprivileged user who may not tamper with the installation
- Firefox and Thunderbird can not automatically update local installation
- you do not want to run Firefox or Thunderbird to check for updates