High CPU/resources usage when lots of tabs are open
This screenshot from "about:performance" illustrates Tab Center consuming a lot of resources, function of the number of tabs you have open (as you can see in the foreground with my "simple tab groups" popover, I have about 240 tabs open in the currently focused group, although only 2-3 of them are currently active / "loaded in memory".
TabCenter is probably doing "something" to monitor the state of those tabs periodically? It might be doing too much work / repainting something, apparently 120 times per second.