Your proxy settings will depend on your provider but if you search for network.proxy you’ll see all the setting you need in there. You’ll connect either through http (ip+port) or socks. Socks adds an additional layer of authentication which is generally preferred but likely won’t be offered by free options.

Yes, your proxy service will absolutely see what sites you are visiting. None of these suggestions will protect you from a malicious proxy service. Https is still honored assuming the end point is using a valid cert and your proxy has not tampered with it in any way. If the cert gets altered you’ll get a warning from your browser, you then have to trust yourself to know when to back out.

Unfortunately container tabs are not yet supported for Android Firefox. FoxyProxy is by no means malicious, it certainly has good intentions and for the most part it does what it says it does. The problem is that due to many fundamental design choices it is too easy for information to leak. Plus the URL regex matching can be very finicky to work with. I used FoxyProxy for years but gave up on it after a while since I could never get a consistent and reliable experience out of it.

At this point I just alter the proxy settings in Android ff directly - no extension. Unfortunately ff profiles are also not supported on Android yet so if you don’t want your main browser to always be attached to a proxy you can install other releases of ff such as Nightly and just configure that with proxy settings. If I am recalling correctly, you can also configure ff to apply proxy to either normal or private browsing too.

Word of caution, If you are actually staying within the Onion network then sure Tor is a great option… The problem is most users just use the exit nodes to reach the clear web. This is a convenient feature of Tor but it’s also the least secure use case. There are a very limited numbers of exit nodes so they are often overused and the majority of them are maintained by government controlled entities since it takes a certain level of legal protection to operate an exit node.

FoxyProxy has many DNS leaking bugs associated with the extension, especially when using SOCKS5 proxies. That extension has not been a recommended choice for a while now.

As others have said, a free proxy is not a good alternative, they are harvesting just as much data as your ISP, if not more (and possibly selling the info back to your ISP). Free proxies also have little incentive to be honest so there is a higher chance they could also be manipulating your traffic in various ways.

A better solution for mitigating data harvesting from your ISP is to just simply adjust your personal DNS settings. This can be configured globally on your router sometimes and/or each client device. Change your default DNS to a more privacy conscious provider such as Mullad, Quad9 or even Cloudflare. Those DNS providers also offer the option of making encrypted DNS requests using DNS over TLS (DoT) and DNS over HTTPS (DoH) which can be configured in your browser and sometimes your router.

At the end of the day, your ISP will still know you connected to a specific end point but they can’t determine what exactly you are doing there, they only know you connected to something like Lemmy.world but would not be able to determine which communities you are visiting.

If a proxy still feels like the only solution then just buy a VPN subscription from a reputable source, its usually pretty cheap and way more effective at preserving privacy and security than any free proxy that is available. Mullvad is generally a pretty good and inexpensive choice plus they also have pretty decent proxy support.

As an alternative to FoxyProxy, check out the extension Container Proxy which allows you to containerize a tab and route all the traffic through a configured proxy which can also be configured on a site-by-site basis. Still, not perfect, but certainly a step above FoxyProxy.