If you love ColorfulTabs like I do and don't want to live without it, you have 2 choices. Both require ditching FF Quantum.
1. If you care about security more than speed, then as others have said, run FF ESR with CT 32.2.3. If you do this, disable auto-updates to CT.
2. If you care about speed more than security, run FF 56.0.2 (the last update before Quantum) with CT 31.2.0. This gets you the benefit of the Firefox multi-process mode, which greatly improves the speed and memory usage of the browser at the cost of being stuck in a static configuration with no security updates. If you do this, disable auto-updates to both FF and CT. This is the config that I use every day.