firewall – Access blocked services through a squid proxy?

I need some help.
I deployed a simple squid proxy on an aws instance, I know it works cause when i check my ip address it shows the ip address of the aws instance.
how ever the proxy seems to only work in special cases.
let me explain.
Twitter has the provision to add a proxy to their app.
So when I add the proxy details it works fine, I can read my tweets not need for full a VPN.
However, adding the proxy setting to firefox has an funny result.
Googling my ip address shows that traffic is going through the proxy, since it reflects the ip address of the aws instance.
Despite this, traffic from blocked websites still seemed to be blocked
How is Twitter able to work well with the proxy and Firefox cannot?
Can Firefox do what twitter does with this HTTP/HTTPS proxy of mine?
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