I see exactly what you're talking about (quite noticable on the 'a' characters) and I wish somebody could explain why Firefox is rendering like that, and if it's a Windows platform specific issue.
Thanks. I've found it futile to argue with people about font rendering over the years. It's always like people are just in denial of reality. Which I feel is emblematic of how Firefox (and Linux, and lots of other libre software) lose desktop market share, IMO - by denying the reality everyone else sees.