When AOL first announced they were discontinuing Netscape, they recommended Firefox (a logical choice for many reasons). Since then, they’ve also started heavily promoting Flock—to the point of offering seamless upgrades from NS8 to Flock. (
In theory, anyway; I fired up the copy I had for testing and couldn’t get it to do anything but update to the most recent 8.x version. Confirmed. I let it sit open in the background for a while, and it eventually popped up the offer for 1-click Flock migration.) Netscape 9 has an update notice that offers to download Flock or Firefox.
The key issue, of course, is moving as many users as possible from a discontinued browser—there’s no doubt that security holes will be found in it over time—to one that is actively maintained.
Why Flock, specifically? Well, sticking with the same toolkit and user profile makes migration easier, so that narrows the field to Firefox and Flock. (Not sure about SeaMonkey’s profile.) Since Netscape 8 and 9 were big on integrating with websites, Flock’s “social browser” seems a slightly better fit. And it turns out most of the Netscape 8 team went on to build Flock. Talk about social networking!