I tried to download firefox nighly to test it using Orion and the website detected the browser as an old verion of MacOS, it would let me download the latest version.
Try download firefox nightly from the mozilla website.
https://www.mozilla.org/en-US/firefox/channel/desktop/
0.99.129-beta
Sequoia (15)
Able to reproduce.
Orion Version 0.99.129.1.1-rc (WebKit 621.1.2.111.4):
Safari and Safari TP:
quick user agent check on both safari and orion:
orion (latest):
custom user agent is set to off.
safari (latest):
pay particular attention to the 'Version/XX.X Safari' part of the user agent string
note i'm on macOS 15.1 (24B83)
Fixed on 129.3-rc, coming to beta soon 
