User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.92 Safari/537.36

Steps to reproduce:

I have addin - download manager.
If my addon captures the download, it cancels its processing for firefox.
The new Firefox 75 version brought the problem - After the capture of the download fiorefox displays a blank page.

To properly capture and manage download Chrome browser has a feature
browser.downloads.onDeterminingFilename.addListener (onDeterminingFilename);
Unfortunately, you have refused to support it because of weak demand.

browser.webRequest.onHeadersReceived.addListener(
onHeadersReceived,
{
urls: [ "http:///", "https:///", "ftp:///" ],
types: [ "main_frame", "sub_frame", "stylesheet", "script", "image", "font", "object", "xmlhttprequest", "ping", "csp_report", "media", "websocket", "other" ]
},
['blocking','responseHeaders']);
function onHeadersReceived( req )
{
return { cancel: true };
}

Actual results:

a blank page shows.

Expected results:

The request initiator page must remain visible.
Everything works to the latest Firefox 75 version.

I tried to reproduce the issue on Windows 10 x64 using the latest Firefox Release and Nightly but I couldn't reproduce it.
I installed "Download Manager s3" addon, downloaded a file and it was downloaded correctly without canceling the process in Firefox.

Does this issue also happen with a new and empty profile? Please see https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems#w_6-create-a-new-firefox-profile

Resetting severity to default of --.

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.

It is better to see once than a few times to explain.
https://antdownloadmanager.com/downloads/test/firefox_issue.wmv - video example
https://antdownloadmanager.com/downloads/test/firefox.html - test file

Shows the correct work of Firefox 74 and incorrect 75.
You will see that after the capture of 75 it leaves a blank page on the screen.

Thank you for your time!

Can you find the regression window here please?

(In reply to Tomislav Jovanovic :zombie from comment #5)

Can you find the regression window here please?
Sorry, what is "regression window"?

Because this bug's Severity has not been changed from the default since it was filed, and it's Priority is -- (Backlog,) indicating it has has not been previously triaged, the bug's Severity is being updated to -- (default, untriaged.)

As I mentioned above I couldn't reproduce it from the first time.
Adrey, mozregression can determine a changeset range corresponding to when a problem was introduced.
You can use it via GUI or via command line, here are the steps: https://mozilla.github.io/mozregression/quickstart.html

Let me know if you need more help with this.
Thanks.

(In reply to Hani Yacoub from comment #8)

As I mentioned above I couldn't reproduce it from the first time.
Adrey, mozregression can determine a changeset range corresponding to when a problem was introduced.
You can use it via GUI or via command line, here are the steps: https://mozilla.github.io/mozregression/quickstart.html

Let me know if you need more help with this.
Thanks.

Thank you!
Yesterday I used regressionwindow. I hope my log has reached the developers.

There is a video example of my test here.
https://antdownloadmanager.com/downloads/test/firefox_issue.wmv - video example
https://antdownloadmanager.com/downloads/test/firefox.html - test file

It's easily reproduced every time.
This problem cannot be referred to errors, but it creates some inconveniences, illogicality.

Chrome browser has the same behavior, but it is compensated by the existence of chrome.downloads.onDeterminingFilename.

Hello,

I have managed to reproduce the issue on the latest Release (76.0.1/20200507114007) and on Firefox 75.0 (75.0/20200403170909) as per the reporter’s initial statement, under Windows 10 Pro 64-bit and Ubuntu 16.04 LTS. Also, as per the reporter, I was unable to reproduce the issue on Firefox 74.0.1.
In addition to the above tested versions I’ve also attempted to reproduce the issue on the latest Nightly (78.0a1/20200524212021) and Beta (77.0b9/20200521224544), however without success.

The STR I employed are the following:

1. Install Ant Download Manager (https://addons.mozilla.org/en-US/firefox/addon/antffw/)
2. Install third party app (Ant Download Manager) when prompted (after the add-on installs a new tab opens to inform the user to install the third party app)
3. Download and open the test file from Comment 9 in a new tab
4. Click on any of the links from the opened test file
5. Notice the page going blank as soon as the link is clicked and the download manager UI pops up

See the attached video for more details.

I have performed a regression range on the issue and narrowed it down to https://bugzilla.mozilla.org/show_bug.cgi?id=1603006 (2020-05-25T13:39:37.406000: DEBUG : Found commit message: Bug 1603006 - Ignore allowLinkedWebInFile when documentChannel is enabled r=kmag) with this differential revision https://phabricator.services.mozilla.com/D56832.

This is the corresponding pushlog: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=b0e84820d231a3b5a47f2ea72c384828d91f4c49&tochange=b158903288bb2968dff9e587a3a8ca67f7435e37

I re-tested on the latest Firefox Developer 77.0 beta May 4, 2020.
It was fixed!

I hope this fix will jump without problems into the nearest release.
Many thanks!

If bug 1603006 is what caused this regression, then bug 1634779 is almost certainly what fixed it for 77+.