This issue appears to be related to the "Open File - Security Warning" pop-up that appears after downloading the file. Having this pop-up displayed will put Firefox in a state of freeze until the pop-up is confirmed or declined, on a "bad" build, compared to a "good" build, where the user can complete his tab drag, even outside the window, where he could have control over the new window, even before interacting with the pop-up.
2020-08-07T03:41:08.612000: DEBUG : Found commit message:
Bug 1588975 - Replace ShellExecuteExW with mozilla::ShellExecuteByExplorer. r=aklotz,asuth
The launcher process turns on the `PreferSystem32Images` mitigation policy for
the browser process. Since the mitigation policy is inherited, a process launched
by the browser process also has `PreferSystem32Images`. If an application which
does not support `PreferSystem32Images`, such as Skype for Business, is launched
via a hyperlink, a custom uri, or a downloaded file, it would fail to launch.
Bug 1567614 fixed this issue by introducing `mozilla::ShellExecuteByExplorer` to
`nsMIMEInfoWin::LoadUriInternal`. This patch introduces
`mozilla::ShellExecuteByExplorer` to two more places.
This is invoked when a user opens a file from the Download Library, or a user
opens a downloaded file with the default application without saving it.
This is invoked when a user opens a downloaded file with a custom application
(configured in about:preference) without saving it.
*Why does this patch change worker.js?*
The mochitest dom/tests/browser/browser_test_new_window_from_content.js failed
if it was executed after dom/serviceworkers/test/browser_download.js in the
same batch. This was because browser_download.js launched Notepad to open
fake_download.bin.txt, preventing a new window from being opened in the
foreground in browser_test_new_window_from_content.js.
The test browser_download.js can verify downloaded data without opening an
associated application. So this patch adds the content-type to the response
header in order not to open Notepad on Windows.
Differential Revision: https://phabricator.services.mozilla.com/D52567
2020-08-07T03:41:08.612000: DEBUG : Did not find a branch, checking all integration branches
2020-08-07T03:41:08.615000: INFO : The bisection is done.
2020-08-07T03:41:08.618000: INFO : Stopped
NI me if results appear incorrect or verification is needed.
Thank you for your contributions!