Assuming you are talking about the Chrome/Firefox fixlets for Windows here.
The Chrome fixlets look like they do include servers in the relevance.
The operating systems that the Chrome and Firefox fixlets target are determined by vendor requirements for those applications.
Chrome requirements: https://support.google.com/chrome/a/answer/7100626?hl=en
Firefox requirements: https://www.mozilla.org/en-US/firefox/87.0/system-requirements/
According to the links, Mozilla does not claim server support for Firefox.
If you want to target OSes not officially supported by those applications and assuming the upgrade is the same as it is for desktop, you can make a custom copy of the fixlets and remove the OS relevance.