I happened upon a great way to get your Yahoo! Mail quicker and slicker on older browsers: Treat your Mac like a PDA. Go to This Old Browser for the URL and more on ... old browsers.
Or, as a public service, here's the direct Yahoo URL.
How to make an aging Macintosh work in the world of 21st-century computing, with a focus on a 12-year-old Powerbook 1400cs and a 5-year-old 14-inch iBook G4