In the latest version of Gmail, they introduced a more compact menu system for Reply (All), Forward, Delete, etc. via a drop down menu. Unfortunately, this menu does not work in the latest version of Safari under 10.4.8).
However, the keyboard shortcuts still work, so you can just hit reply, reply all, and forward. Note that you have to have the shortcuts enabled in Gmail's Settings screen for this to work.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20061124065446255