For some reason, whenever I try connecting to certain webpages (ex. YouTube), Chromium always returns an error that says "ERR_CONNECTION_REFUSED".
I've tried switching over to other browsers (Tor, Firefox, Vivaldi, and Opera), none of which work. Interestingly, I can access it from other devices on my network (my phone, for example) or when I boot into Windows 10 rather than Ubuntu, so it can't be a modem/router or ISP issue. Additionally, I'm able to access webpages like https://www.youtube.com but not http://www.youtube.com.
This happens pretty much at random - there's no list of sites that work and do not work.
What could be causing this?
EDIT: Another error has popped up - ERR_CONNECTION_RESET. This occurs in addition to the original ERR_CONNECTION_REFUSED issue.
EDIT 2: Updated to Ubuntu 16.04, but nothing has changed. I still get the same errors.