When I download a file .epub (error rate 1%) or .mobi (error rate 3%) or .zip (error rate 0.2%) to my ebooks folder I randomly end up with "filename.ext" of size 0 and one "filename(1).ext" of the correct size and correct content. That error rate is independent of file size but dependent of the file extension. The download never fails and no file have any defects. Configuration: * Firefox 64bit 104.0 to 106.0.5 on Windows 10 Pro 22H2 * In Settings: Always ask you where to save files is checked * Target folder (confirmed on each download) is a subfolder of Documents * Only antivirus is Microsoft Defender. * The user account is a Local account there is no one drive or other cloud storage solution active. After 3 months of tests, I managed to solve the problem with: about:config and set browser.download.manager.scanWhenDone to false. I tough that option was gone in 2015, but apparently it is back. That is however not a good solution. Test I did: * Adding the download folder as an AV exclusion: no changes. * Disabling extensions: no changes. * Disabling indexing on the target folder: no changes. * Changed targeted folder: no changes. * Disabling the file history backup: no changes. I suspected either a program is monitoring Documents folders for changes and opening the downloaded file concurrently with Firefox. Since disabling Firefox av interface probably seriously modify the timing of directory change notification and Firefox file manipulation, I'm still not sure who is to blame for the problem. If you have any idea on how to debug that, let me know.