Firefox shouldn't be doing that, but you can check your extensions just to be sure.

• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

It is possible that (anti-virus) security software is causing the problem. Try to disable security software temporarily to see if that makes a difference.

Hello cor-el, disabling the AV did not resolved the issue. Refresh firefox did not resolved the issue. Uninstalling firefox, deleting all data under appdata and installing from scratch did not resolved the issue.

Downloading files with AV turned on and using other web browser is working without issues.

You can boot the computer in Windows Safe Mode with network support to see if that has effect.

• https://www.bleepingcomputer.com/tuto.../how-to-start-windows-in-safe-mode/
• https://www.digitalcitizen.life/4-ways-boot-safe-mode-windows-10/