It's annoying when a link opens in a new window when you're used to tabs, so found this userContent.css snippet for Firefox:
/* Change cursor for links that open in new window */
:link[target="_blank"], :visited[target="_blank"],
:link[target="_new"], :visited[target="_new"] {
cursor: crosshair;
}
/* Change cursor for JavaScript links */
a[href^="javascript:"] {
cursor: move;
}
Change the cursor so you know when a new window opens and also indicates if a link is a javascript one which probably won't work if you try to open it in a tab.