Using ctrl-click (but not middle-click) on a "content editable" link, does not currently work with Chromium37, but does work with Firefox39.
Using Middle-mouse-click on links does not work in either browser
Using Right-mouse-click to show the context menu with "Open link in new tab/window" does work in both browsers.
(Prior description had different results for Firefox 22.
Ed notes below, that this is all browser-specific behaviour, and rather than overriding that, we should just solve T56759: VisualEditor: Provide a way (beyond Ctrl-Click, middle-click, or right-click/tab) to open links in another window (Done))