I was a confirmed user of Mozilla Firefox and Mozilla Thunderbird; although I use Window Live Mail too, just for hotmail.. I tried SeaMonkey - an offshoot of the Mozilla Suite as Firefox and Thunderbird are too - some years ago, but it didn't have full support for PGP Desktop (necessary for some of my work), so I forgot about it. I downloaded SeaMonkey 1.1.16 recently, installed it.
I like it. I like browser (Navigator), mail and newsgroups, html composer, address book, and IRC Chat in one program. It uses less ram than the Firefox and Thunderbird duo. It has the essential addons, NoScript, CS Lite or Cookie Safe, and AdBlock Plus;although it doesn't have a full calendar like Lightning for Thunderbird which gives it most of the feature as in Outlook. It does have a calendar, Reminderfox, which should suffice for home computering and probably for most home business. It also has some other addons, though not the extensive choices available for Thunderbird and Firefox. But it has built in features to cover the more important functionality you get from many addons of the dynamic duo. Built in it has Translate Page, Cookie Manager (which you can augment with CS Lite, my favorite, or Cookie Safe), Image manager, Popup Manager, Bookmark Manager, Form Manager, Password Manager, and Download Manager. It is easy to install addons, but to uninstall them easily you have to install the Extension Uninstaller addon. There is an addon available to minimize it to the Tray also. For faster opening you can configure it by a check in a box that keeps a part of it in memory. I don't use it; it opens fast enough for me without that. It supports multiple homepages, as does Firefox. The plugin MultiZilla that gives it even more functionality.
SeaMonkey is my default now, but I use multiple browsers, Firefox, K-Meleon, KM Lite, and IE 8. They are my internet filing system. I used Flock another Gecko browser at one time for social networks, but it used too much of my resources. SeaMonkey supports PGP, as stated above, and security certificates, like Thawte. I sometimes use encryption, and always sign my mail - mostly with my Thawte certs.
SeaMonkey 1.1.16 is light on resources, with all the functionality needed by most and in one application either builtin or by addons, it is secure, AES cipher, 256-bit key. I say that it is worthy of consideration as your default internet application - browser, email, et cetera.
I have an older relative, 96, who uses it without any problems. I installed it for her. she set the default opening to email; she only has to click a button on the email status bar to open the browser. You can set it to open browser first, email first, both, or a box to choose each time. With me looking on she configured it herself. The gui is intuitive. She installed the addons herself, but I suggested which ones.
If you want the simplicity of one unified internet application, I recommend that you try SeaMonkey, especially if you like the old elfish Navigator buttons. (I have them on my K-Meleon and Firefox.) Netscape is bloated, and support for it is ending.