This has been driving me nuts as well. It's not so much that the button to close the tab is on the left, but that the favicon turns in to the close button on hover. It's not good UX in my opinion. I don't think an icon that helps visually identify the tab should also double as the spot to click to close the tab. I instinctively want to click on the first identifying element I see to switch to a new tab and the most visually distinguished element is the favicon. It would be nice if there was an option available to move the close button to the right for users who would prefer that.