There's 2 known issues concerning MacOSX and vz webmail that I am aware of:
1. The Safari web browser on Apple computers is unable to access the Rich Text Formatting option when composing, replying to or forwarding messages. (Other browsers, such as Firefox, do work)
2. If you're using Safari on MacOSX 10.3.9 or earlier, the content of e-mails is not displayed. Upon hitting reply, the message is populated as a reply quote in the new e-mail.
What specifically is happening with yours? (Screenshots would be clutch)
Are your security settings prohibiting external scripts to be ran on websites?
All I can say on that, is the fact that everythign Verizon is geared towards windows.... Mac applications and even Mac friendly webpages have never been a Verizon strong suit or priority...... MY only suggestion is firefox for Mac.... See if that helps
Otherwise, use MacMail or another email client for email instead of the web-based email interface, and set it to leave a copy on the server, that way if need be you can still check/reply to email from the web based interface in a pinch.