BTW, same behaviour when running the snipped on chrome://version or similar (not that this would affect anyone). But should allow to segment without installing any extension.

Is not limited to blob-urls, also affects filesystem:xxx URLs.
So it does not seem possible to use the Filesystem API + trigger a download from an extension context in Chrome 65 anymore like this (works fine from regular webpage):

http://jsbin.com/hatuso/1/edit?html,js

Does not affect http-URLs served with a content-disposition: attachment header

Able to reproduce the issue on Windows 10, mac 10.12.6 and Ubuntu 14.04 using chrome reported version #65.0.3319.0.

Bisect Information:
=====================
Good build: 65.0.3309.0    
Bad Build : 65.0.3310.0   

Change Log URL: 
https://chromium.googlesource.com/chromium/src/+log/cbce1149c9ae08297b816effbf456c02f97df8db..f2d2fe87028de36a489f7db3f5fb28da2e9d9b2b

From the above change log suspecting below change
Change-Id: I508d7abe1cba9b75d65132b0688984cdebfc6fd4
Reviewed-on: https://chromium-review.googlesource.com/758236

jochen@ - Could you please check whether this is caused with respect to your change, if not please help us in assigning it to the right owner.
Note: Adding stable blocker for M-65 as it seems to be recent regression. Please feel free to remove the same if not appropriate.

Thanks...!!

Example snipped for filesystem:* URLs (same behaviour):

function downloadUrl(url) {
  console.log('downloading', url);
  let linkEl = document.createElement('a');
  linkEl.setAttribute('download', 'foo.webm');
  linkEl.setAttribute('href', url);
  linkEl.dispatchEvent(new MouseEvent('click'));
}


async function createFile() {
  let fs = await new Promise(r => webkitRequestFileSystem(window.TEMPORARY, 1 * 1024, r));
  let fileEntry = await new Promise(r => fs.root.getFile('foo.webm', {create: true}, r));
  let fileWriter = await new Promise(r => fileEntry.createWriter(r));
  let writeDonePromise = new Promise(r => fileWriter.onwrite = r);
  fileWriter.write(new Blob(['some content']));
  await writeDonePromise;
  console.log('created file');  
  return fileEntry;
}


async function downloadFromUrl() {
  let fileEntry = await createFile();
  downloadUrl(fileEntry.toURL());
}
downloadFromUrl();

I believe this is a duplicate of  issue 798705  - can you verify whether it reproduces on ToT?

Does not reproduce on 65.0.3321.0 anymore, so it's duplicate. Sry, did not find that one.

thanks for verifying!