Download of blob url is not working with elem.click()

[karlcow]

Steps to reproduce (Firefox on iOS v34)

1. Go to https://cubari.moe/read/gist/JG33X/9/1/
2. spot the first toolbar with the down arrow, the link icon and the right angle arrow icon
3. tap on the download button

Expected:
A menu is displayed asking to save the file 9.zip in Downloads

Actual:
a progress counter is shown but the modal menu doesn't appear.

The progress counter is client side and doesn't mean anything.
The real download happens with this piece of JavaScript.

  function initiateDownload(url) {
    let elem = window.document.createElement('a');
    elem.href = url;
    elem.download = Reader.SCP.chapter + '.zip';
    document.body.appendChild(elem);
    elem.click();
    document.body.removeChild(elem);
  }

It creates an html element with a blob url

<a href="blob:https://cubari.moe/771fec36-937a-c841-8e4d-c189a5d04c62" download="9.zip"></a>

that it clicks with elem.click()

This is not happening in Firefox iOS.

see the full diagnosis at webcompat/web-bugs#75388

┆Issue is synchronized with this Jira Task

[ksy36]

There is a similar issue in webcompat/web-bugs#75965, but with an image. I've created a reduced test case for it: https://codepen.io/ksy36/pen/gOmdJWW

[karlcow]

@ksy36 There is an error message in the console for the reduced test case.

Cannot access blob URL “blob:https://cdpn.io/a13d0093-357a-f548-a2bb-e5c63c308194” from a different agent cluster.

This leads to this error message in the source code.

which is associated with Add a console warning when blob URL partitioning is applied itself created because of Blob isolation regresses sandboxed iframe downloads and Can't export Google Contacts on Nightly.

[karlcow]

I should have clarified in the previous comment in the case of gecko.
But this might lead us to the right thing. Specifically WKWebView does not support blob: URLs as href value in anchors with download attribute

[karlcow]

I added a comment on https://bugs.webkit.org/show_bug.cgi?id=216918#c4

[github-actions]

This issue has been automatically marked as stale. Has the issue been fixed, or does it still require the community's attention? Please leave any comment to keep this issue opened. It will be closed automatically if no further update occurs in the next 30 days. Thank you for your contributions!

[ravicious]

I believe it still doesn’t work, at least the example from the first post.

[clemlesne]

Maybe related to #14053.

[karlcow]

@denschub and others could you double check this might have been fixed.