can't access some websites

I have this weird problem that causes chrome and firefox to download some pages (like: https://www.mozilla.org/en-US/firefox/new/ or hwzone.co.il - please notice this happens only on some websites and not all)
instead of simply viewing them. the file that get downloaded isn't even a html file, but an unknown format.

In Internet explorer the pages will show a weird € until i flush the dns cache and then internet explore will start displaying it until the next time (chrome and firefox still wont show the pages)

using developers tools I managed to find that the error I get is 407.

my computer is windows 10 (enterprise) and is part of a domain that uses a proxy server. only my computer is suffering from this problem (I checked my user on a colleague computer, and had my colleague test my computer), which is part of the reason I am convinced that this is a windows problem and not a browser problem. It is a clean installed computer so I don't believe it is a corruption, virus or the sort.

I can't determine what the problem is, can anybody help?

Do you use other download manager that installs add-on\extension into the browsers besides of the default download manager? If yes, try to disable the add-on\extension for a test.

I don't have any download managers.

update:
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flushing the dns cache doesn't help any more with internet explorer anymore.
it seems that this problem randomly regresses back into not working at all

also- I can only capture the 407 error with ie and firefox not with chrome. chrome will simply download that weird file and not capture any network traffic.

I also discovered that I get a 301 error.