The portable builds are fully portable, the profile directory is inside the browser folder. It does not touch appdata at all.

Changes on top of the previous 125.0.2-2 build:
Scrollbar supposedly looks better idk nara did it so I did it.
Menu list text is more accurate.
Better private browsing tint for classic theme, showing the theme colors.
Option to force enable caption bar transparency.
JPEG XL transparency and animations work now.
Browser should register with JXL files if default.
Red gradient private browsing background is toggleable with r3dfox customizations toggle.
Private browsing advertisements should be removed now.

Haven't tested on XP/Vista (extended kernel) nor have I stability tested.

Please let me know what bugs or issues you encounter with it.