I can just second the idea of making it configurable, but there must be a consolidation too in the moment it's configurable - Otherwise you start accumulating lots of settings around design details that an average user expects to come out of the box ...
Firefox 157's rounded tabs are a regression, not progress. This is a direct copy of Chrome's aesthetic — and a bad one. If I wanted Chrome's look, I'd use Chrome. The rounded tab shape has no visual connection to the content area below it. It floats....
