Save page as... failing reproducible.
1. Right click in a website and "Save Page as.." it. - (image one.jpg) 2. Observe if it gets a yellow point for a failed download in "Downloads" (ctrl-j) - (image two.jpg) 3. Manual retry. Success! - (image three.jpg)
But you will never ever get Firefox work on the first try to save a page. This doesn't work for years.
Why? Even with deactivated addons/safe mode.