Hide "List all tabs" when the tabs don't overflow

A new Firefox (or is it chromium?) innovation is to add an icon at the end of the tab bar with a dropdown showing a list of all tabs open.

It's possible only display the icon when tabs are overflowing by setting browser.tabs.tabmanager.enabled to false.

This was the default behavior until ESR 115.

It feels to me that it may be better to keep that option, because it keeps it cleaner for those who don't tab hoard and will appear when you need it.

If users really want it, then we could change it a that point to default.