>>> My Info: Win7_64, Nightly 49, 32bit, ID 20160526082509 STR_1: 1. Open new Firefox window 2. Open url [1] in a new tab in that window 3. Click on the link on the page, then in less than 3 seconds switch to another Firefox window 4. Wait 3 seconds AR: Firefox window opened in Step 1 is now focused and brought to foreground ER: Firefox window should stay in background > [1] data:text/html,<a onclick="setTimeout(function(){location.href='https://bugzilla.mozilla.org/attachment.cgi?id=8730849'},3000)">Link</a> STR_2: (reference of good behavior) 1. Open Windows Explorer. Launch Firefox. 2. Open url [1] in a new tab in Firefox. 3. Click on the link on the page, then in less than 3 seconds switch to Windows Explorer window 4. Wait 3 seconds AR: Firefox window opened in Step 1 stays in background, just as expected Note: 1) Originally, I encountered this bug many times when the page/Firefox were lagging, so after clicking a button to download the file (e.g. on page http://ssyoutube.com/watch?v=mD3v1B_aXw0) I had enough time to switch to another Firefox window and start doing other important stuff... Only to be interrupted by Firefox: It completely hides current page and shows another page from another window 2) If you disagree with "ER", consider this bug report for implementing the same behavior in STR_2 I didn't mention that in expected result (ER), because while I expect consistency, I can't imagine that the obtrusive behavior described in STR_1 is intentional.

User Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:53.0) Gecko/20100101 Firefox/53.0 I have verified this issue on latest Nightly (Build ID: 20170116030326) and latest Firefox release v50.1.0 and it is reproducible. I have followed the steps from Comment 0.

Wasn't able to reproduce on mac. Though it does bring up the Save File dialog - but I guess that's expected. It is focusing the other window on Windows, then that's pretty annoying.

Ok, so, the save dialog does also steal focus on Mac... like if you are typing into an input field. This is UX issue tho.