The address wasn’t understood
Firefox doesn’t know how to open this address, because one of the following protocols (nxm) isn’t associated with any program or is not allowed in this context.
You might need to install other software to open this address.
what the fak
Wow, that's some way to unearth a dead and buried topic with a new problem completely unrelated...
What button or link were you trying to click there? 'Cause "nxm" is the protocol/file type used for "manager" downloads, so it should've been one of the "download with manager" buttons, which will of course only work once you installed said mod manager(s).
Do you have Vortex installed (or Nexus Mod Manager, the previous one) already? If you don't have any mod manager installed, then pressing the buttons meant to start the manager will of course not work. If you do have a mod manager installed and it's still not working, then either the association was never implemented correctly or got lost during some changes to your OS or software later on. Most managers will have an option to re-associate the file type/protocol with themselves, so your OS and browsers will know again what to do with these.
If you're having problems getting Vortex to work, the fine folks over here will help you along: https://forums.nexus...vortex-support/
If you're having trouble with the no longer officially supported Nexus Mod Manager, then you can ask the community for help here: https://forums.nexus...-beta-feedback/