[adamzochowski]

There was a proxy, proxomitron in early 2000s, that allowed you to change the html/js as it went through the proxy. people used it for adblocking and removing page annoyances, like removing sounds / animated gifs / etc. Here is a list of random old filters people had built at one time: https://proxomitron.info/45/help/Default-Web-Filters.html

[dredmorbius]

There were numerous of these.

Privoxy, dansguardian, Squid (AFAIR), and others.

The notion that SSL/TLS means that ONLY the webserver origin and web browser client are permitted to see or mitigate content ... is itself harmful. Trusted proxies under your control do have a place, though yes, that introduces new points of contention as well.

[captn3m0]

I used to swear by Privoxy till the internet realised HTTPS was actually important and it stopped working everywhere.

[dredmorbius]

Largely the same. Privaxy actually looks pretty sweet in that regard.