Squid TCP_DENIED/403 4037 GET http://detectportal.firefox.com/success.txt - HIER_NONE/- text/html

Solution 1:

line 1195 - http_access deny all

That's a catch-all rule that is going to block traffic that hasn't been specifically allowed in the config. Which, if this is your whole config, is nothing. Looks like you've got a stock config that will require some allow rules. Alternatively, modify the http_access deny all and change the deny to allow

If you intend to have authentication setup, you can do something like this:

### enforce authentication
http_access deny !auth    # deny anyone that isn't authenticated
http_access allow auth    # allow authenticated users
http_access deny all      # final catch-all that should never actually be met.

If you haven't setup authentication yet, then you just need this:

http_access allow all