if you intend to use the launcher, which as a reminder is going to be deprecated later this year, you could give chromium based browsers first. there were reports of other users having better luck as opposed to firefox.
that said, if you think getting the source code from git directly, you can refer to the steps to setup KIT based apps such as Isaac Sim or Composer here -
Isaac Sim:
Download Isaac Sim — Isaac Sim Documentation
Composer:
kit-app-template/templates/apps/usd_composer at main · NVIDIA-Omniverse/kit-app-template · GitHub
and the step by step instructions can also be found in another thread:
I have a question about the end of support for Omniverse Launcher - Help & Feedback / Omniverse Technical Support - NVIDIA Developer Forums