Previously the add-ons manager would open in the foreground but now it opens in the background for me. Guessing this is a change from bug 593687. Was it intentional? Seems wrong to me.
Maybe the setting has nothing to do with it, seems to always open in the background for me.
The pref controlling this is browser.tabs.loadBookmarksInBackground. Bug 610203 adds an inBackground parameter that switchToTabHavingURI could use to override the pref.
Seems a little wrong but a non-default setting so not worth much time right now I guess
Created attachment 565525 [details] [diff] [review] patch