Affected versions

• latest Nightly 79.0a1
• Beta 78.0b9
• Release 77.0.1

Affected platforms

• Windows 10 x64
• macOS 10.14
• Ubuntu 18.04 x64

Steps to reproduce

1. Launch Firefox.
2. Navigate to http://www.mixedcontentexamples.com/Test/RedirectToHttps in a new tab.
3. Access again http://www.mixedcontentexamples.com/Test/RedirectToHttps in the same tab.

Expected result

• The page is redirected to HTTPS, the lock icon is not crossed out and the connection is secured in the control center.

Actual result

• The page doesn't get redirected to HTTPS, the lock icon is crossed out and the connection is not secured in the control center.

Regression range

• The bug seems to be an old regression, I was unable to reproduce it on a Nightly build 58.0a1 from 2017-10-10. I'll try to find a regression range asap.

Additional notes

• It seems that this issue is somehow intermittent, sometimes to page is correctly redirected after a refresh or a browser restart.
• I think this bug can be marked with a S3 severity, given the fact that it can also be reproduced on older Fx releases.

I think this bug is a duplicate of bug 1628133. It seems like a website problem because I can also reproduce with Chrome and IE11.

https://bugzilla.mozilla.org/show_bug.cgi?id=1628133#c4

Thanks for filing the bug. We have seen this before, I'll mark it as a duplicate (See Bug 1628133).