downloads end just before the end of the file, regardless of file type/size. also pages don't fully load first time (have to reload) regardless of the website.
I am downloading from various sites but recently the downloads end before the end of the file (but always at about 97-98 percent). The type/size of file does not matter, nor does the website. In addition, webpages don't fully load on the first try (almost always) and I have to reload to get the full page, regardless of the site. This problem started about two weeks ago and lasted several days. Now it started again. RAM/CPU/storage all OK
It is possible that your anti-virus software is corrupting the downloaded files or otherwise interfering with downloading files by Firefox.
Try to disable the real-time (live) scanning of files in your anti-virus software temporarily to see if that makes downloading work.
See "Disable virus scanning in Firefox preferences - Windows"