Why does the moonbeam/moonriver polkadot-js websites not have an extrinsics developer menu? The chain state can be queried, and RPC seems there.
I'm just curious.
The apps only show certain functions, including the extrinsics tab, when you have at least one account.
Because Moonbeam uses Ethereum-style accounts instead of Polkadot accounts, your existing Polkadot account set to be used on all chains doesn't count as a Moonbeam account.
Instead, you will need to create a new account in the polkadot.js apps for Moonbeam. Once this is done, the extrinsics tab appears just as it does for other chains.
Here's a trick that I learned: even when a particular parachain does not explicitly show the extrinsics menu item on polkadot.js.org/apps, the webpage is still accessible if you simply add #/extrinsics
to the end of the URL, and it is fully functional as well! See the screecap below: