I've used SeaMonkey since it was just Mozilla until recently. The reason I finally dropped it was recent issues with updates that screwed some things up and I got tired of it. I've moved everything that's 64 bit to Waterfox and those who are on 32 bit Win are running Firefox. I too can't stand the 'Chrome' look and found some excellent plugins that make the interface more like SeaMonkey.
First, right click in the icon area (right of URL bar) and select "Menu" and "Bookmarks Toolbar" (if you desire them).
Select Open Menu (icon w/ three horizontal lines to the far right of the URL bar) and under General, set your home page and set "When Water/Firefox starts" to "Show my windows and tabs from last time". Then uncheck "Don't load tabs until selected". Go ahead and configure the other options (on the left) as you wish. Close the Options tab.
Select Open Menu again and select Customize. In the Customize tab, drag the 'Open a new tab' icon (+ symbol) to the left side of the screen (left of the leftmost tab). Grab a theme if you so desire!
Select Open Menu again and then select Add-ons. In the Add-ons tab, search for and load the following plugins:
Adblock Plus
Buttons Back (puts the Home, Back, Forward & Reload buttons back)
HTML5 Player for YouTube
New Tab Homepage (defaults to your home page if you open a new tab)
No Script
SuperStop (shift+esc keys stop page activity)
Tabs On Bottom (moves the window tabs back to right above the page)
With this setup the Foxes are tamed...lol!
