FF4 is OK, but they have made some changes I absolutely hate. They hide some menu items, for no particular reason.
And they swapped the "New Window" and "New Tab" items in the right click.
People respond "install the menu-editor addon" but that's a big mistake. It does not work well. My right menu flies off to the side, or strobes randomly, when I have that open. The ME author says he won't fix it because it conflicts with too many other programs.
Luckily, there is a more direct fix that does not require an addon. In the file "userChrome.css" insert the following lines. (If file does not exist, create it).
The file is under your user profile: .mozilla/firefox/whatever.default/chrome
$ cat userChrome.css
@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */
/* Always show all hidden menu entries */
#navigator-toolbox menuitem[class="show-only-for-keyboard"] { display:-moz-box !important; }
#contentAreaContextMenu > * { -moz-box-ordinal-group: 2; }
#context-openlink { -moz-box-ordinal-group: 1 !important; }
