Tools > Options -> Tabs

or Options thru the "3-bar" Open Menu button > Open Options

The setting in Tools > Options > Tabs: "New pages should be opened in": "a new tab/window" is for links that specify a target window to open the link. That option allows to divert such links to a new tab instead of a new window. Links that do not specify a target always open in the current tab unless you override that with a middle-click or Ctrl left-click (new tab) or Shift left-click (new window) or via the right-click context menu. JavaScript running on the page or an installed extension can also change (override) the default behavior. This applies to bookmarks and other links as well, i.e. you can middle-click the View Image item in the right-click context menu of an image or middle-click the Reload button on the location bar to get a new tab with that link. Left-click a JavaScript link (e.g. you see "#" on hover) to avoid getting a blank tab.

• http://kb.mozillazine.org/browser.link.open_newwindow
• http://kb.mozillazine.org/browser.link.open_newwindow.restriction

There is an option to "Open new windows in a new tab instead" but NOT to "open in new windows". Firefox 31.0. I don't want a new tab.

You can divert a new tab to a new window by setting the browser.link.open_newwindow pref to 2 on the about:config page.

• http://kb.mozillazine.org/browser.link.open_newwindow
• 1: current tab; 2:new window; 3:new tab;

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

• http://kb.mozillazine.org/about:config