After updating from FF52 to FF53, the logic for the setting Tabs -> Tab Opening -> Focus new tabs from: -> Links flipped on me - when unchecked, middle-clicking on a link will immediately switch focus to the new tab, and vice versa. This is opposite to the expected behavior. Disabling e10s had no effect. Have not tried turning off all other addons yet.
EDIT: Actually this is not correct... it just seems to behave erratically. After posting this, it somehow returned to the correct behavior. But then I found that I can reproduce it by restarting the browser.
After updating from FF52 to FF53, the logic for the setting
Tabs -> Tab Opening -> Focus new tabs from: -> Linksflipped on me - when unchecked, middle-clicking on a link will immediately switch focus to the new tab, and vice versa. This is opposite to the expected behavior. Disabling e10s had no effect. Have not tried turning off all other addons yet.EDIT: Actually this is not correct... it just seems to behave erratically. After posting this, it somehow returned to the correct behavior. But then I found that I can reproduce it by restarting the browser.