Welp, yeah, that was it!
I wonder, why would I have it off? I never touched that setting, 
How are your browser.tabs.groups options looking? Mine look like this:
| field | value |
|---|---|
| browser.tabs.groups.enabled | false |
| browser.tabs.groups.smart.enabled | false |
| browser.tabs.groups.smart.optin | false |
| browser.tabs.groups.smart.userEnabled | true |