I recently switched from Chrome to Firefox as part of an ongoing de-Google effort… and, honestly, I found it fairly easy. The two things I missed and found solutions for were:
Profiles - I just use the built in profiles with the Profile Switcher extension
Casting to Chromecast - I use the fx_cast extension and actually find it more reliable than Chrome’s casting!
Other than those, I’ve found it to be a very comfortable, familiar experience.