Mail links open new windows in Chrome instead of new tabs
I have High Sierra running on a mid-2010 Macbook Pro, and Chrome 61.0.
Recently, when I click on a link in an email message, Chrome (which is my default browser) opens a new (blank) tab in a new window instead of opening the link in a new tab in the active window.
Since this is a relatively new occurrence and I haven't changed or done anything which should cause this behaviour, where should I look for the setting to ensure that links are not only opened but also opened in the correct place?
MacBook Pro, macOS High Sierra (10.13.2), Mail 11, Chrome 61