Will Dormann made a nice post with Firefox settings that a security-/privacy-conscious user may want to enable:

If anybody else is making the switch to (or back to) Firefox, there are a few settings that a security-/privacy-conscious user may want to enable:

1. Enable the Block AI enhancements toggle to disable all AI-related nonsense globally.
2. Disable Telemetry & Data Collection.
3. Disable "Firefox Home"
4. Use "Strict" tracking protection
5. Enable HTTPS-only mode

Bonus:
In about:config, set:

• privacy.resistFingerprinting: true
• media.peerconnection.enabled: false
• geo.enabled: false