Browser downloading blank .HTM files

Both of my Firefox based browsers (latest ESR and r3dfox) occasionally and without notice download a blank .HTM file to my download folder. Maybe once or twice a day. They all have a different random file name.

eg: yMHmvXVM.htm

I've checked my browser history to try and correlate when it happens with computer activity and it's never when I'm looking at the same site. Could be one of dozens that I visit regularly.

I've done full scans with my a/v and Malwarebytes and scanned the files online with multi-a/v scanners and they're ok.

Any ideas? Google doesn't help.

Doesn't seem to happen with other non-FF browsers.

EDIT: I'm going to disable my browser extensions/addons that I use on both browsers one at a time to see if that does anything.

Do you have the same set of extensions on both Firefox based browsers? I have not had this happen with Firefox or Waterfox, but I do not use any extensions.

Identical. Incl uBlock. I've eliminated two of four so far.

It seems like this add-on was responsible for those files. They're harmless fortunately so I'll just leave it alone. No one else has mentioned it on their web page though.

Attachment 15970

Cool.... At least you have an answer.