We will need more info to help you... Provide an example link of what you are downloading that shows the slow speed. Are you on WiFi or Lan? Who are you using for DNS Did you clear your browser cache and dns cache?

Thanks for getting back at me! I am using a Gigabit LAN connection, so there should be not issue of "limitation" here. My DNS-settings are as follows: IPv4 8.8.8.8 and 8.8.4.4 Ipv6 2001:4860:4860::8888 and 2001:4860:4860::8844 Its the Google ones.

Both caches are cleared, too!

I tried download various files from various websites and none were quickly downloaded, sadly. Just as an example, I chose one from here: https://sample-videos.com/download-sample-zip.php. See the attached screenshot of how that went.

ISP Speeds are based on ISP providers and their plans. There's not much that Firefox can do as it's at the mercy of ISP speeds. So unless there is malware/virus infection causing the issue there not much that Firefox can do to ISP access speeds. 1Gigabit connection Lan means nothing for ISP speeds unless you have 1Gigabit ISP bandwidth. LAN speeds are just local speed it has nothing to do with your ISP internet connection. So know that LAN speeds aren't ISP Speeds those are two different Network connection speeds and not mutual.

That’s true but I do receive the full volume, so to say. Speed tests are showing that everything that should reach me does in fact reach me. Steam, ORIGIN, Mega, all those download services work blazing fast - as expected with a 600Mbps line. It’s just that Firefox (and Edge, too) are incredibly slow…

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/

Thank you - I shall try it and come back to you later.