How to set up Proxy in Firefox browser on Android

Short and simple guide without FoxyProxy and other overwhelms.

1. Install Firefox Nightly for Developers, it's not possible changing developer configurations in regular Firefox application.
2. Enter about:config in address bar.
3. Set HTTP proxy IP: network.proxy.http
4. Set HTTP proxy PORT: network.proxy.http_port
5. Set HTTPS proxy IP: network.proxy.ssl
6. Set HTTPS proxy PORT: network.proxy.ssl_port
7. Set: network.proxy.type to 1 (means switch ON)
8. Optionally: network.proxy.no_proxies_on add websites that bypass proxy

Enabling proxy for all applications

There's the easiest way to enable Proxy for all mobile traffic

Settings > Mobile network > Mobile data > Access Point Names (APNs) > [Your regular Internet] (info) > set Proxy, set Port (bypassing certain websites is not possible)

and Wi-Fi

Settings > Wi-Fi > [Your Wi-Fi connection] > Modify network > Proxy > Manual > set Hostname, set Port

Why Proxy?

Because, you don't really need VPN in most cases.

For example, proxy is more suitable choice for Mobile devices over VPN because it doesn't require additional software running in background and consuming your battery. Also it has higher speed (about x2 uploading and +10% downloading versus the fastest VPN for now Wireguard).

Although it's less secure than VPN, it's still optimal for such trivial task as bypassing local blocking.