Firefox broke all the useful URL bar shortcuts and replaced them with text replacers.
control-enter used to open the URL in a new tab, with control-shift-enter opening it in a new tab in the background, now it adds www. and .com to whatever is in the location bar. If someone wanted those they would type it, or the built in system would add those if what they typed was not a proper domain.
shift-enter used to automatically download an URL, whatever it was, a file, a webpage, whatever. now it adds www and .net.
alt enter used to do something useful too I just don't remember, now it opens a webpage in a new tab, albeit without being able to use the shift modifier to not automatically switch to the tab.
Worse, you used to be able to use these modifiers with bookmarks or on any link you clicked. Now you can't even middle click a bookmark and have it open in the background even while middle clicking links does. A lot of functionality that used to exist doesn't, and when it is there, It's totally inconsistent.
And if you go and report these issues it won't even let you do that. http://i.imgur.com/S8D8t.png
Cookie management is a pain too, in seamonkey, if you want to change a sites cookie permissions, you go to a menu->sub menu->allow/deny cookies. In firefox you have to right click, open page info, select the privacy tab, click allow/deny cookies, then close the window, which is 3x as long, for a browser that's supposed to care about your privacy.