diff --git a/README.md b/README.md
index 418bba9..7f6847b 100644
--- a/README.md
+++ b/README.md
@@ -2395,6 +2395,8 @@ view would leave a wallet one click from deletion.
     - Raw data: full calldata displayed inline (shown if present)
     - Password input and an error line
     - "Confirm" / "Reject" buttons
+- **Behavior**: Every etherscan link on the screen opens the explorer of the
+  network the transaction was populated on, whichever network is active.
 - **Transitions**:
     - "Confirm" (correct password) → decrypts and signs the transaction it was
       shown, exactly as shown, hands the signed transaction to the background to
diff --git a/src/popup/views/approval.js b/src/popup/views/approval.js
index 6911927..0344652 100644
--- a/src/popup/views/approval.js
+++ b/src/popup/views/approval.js
@@ -58,9 +58,15 @@ const { notify, runtimeApi, sendMessage } = require("../../shared/browserApi");
 
 const erc20Iface = new Interface(ERC20_ABI);
 
-function approvalAddressHtml(address) {
+// The link opens the explorer of the network with `chainId`, or of the active
+// network when none is given. A chain id that names no network has no
+// explorer, so the address is drawn without a link.
+function approvalAddressHtml(address, chainId) {
     const title = addressTitle(address, state.wallets);
-    return renderAddressHtml(address, { title });
+    if (chainId && !networkByChainId(chainId)) {
+        return renderAddressHtml(address, { title, noLink: true });
+    }
+    return renderAddressHtml(address, { title, chainId });
 }
 
 // The amount line for a decoded ERC-20 call. With a known scale it is the
@@ -338,8 +344,14 @@ function showTxApproval(details) {
         };
     }
 
+    // Every address link on this screen opens the explorer of the network the
+    // transaction is for, which the Network line names, whichever network is
+    // active.
     $("approve-tx-origin").textContent = details.origin;
-    $("approve-tx-from").innerHTML = approvalAddressHtml(details.approvedFrom);
+    $("approve-tx-from").innerHTML = approvalAddressHtml(
+        details.approvedFrom,
+        approvedTx.chainId,
+    );
 
     // Show token symbol next to contract address if known on the network the
     // transaction is for
@@ -349,7 +361,7 @@ function showTxApproval(details) {
         if (symbol) {
             toHtml += `<div class="font-bold mb-1">${escapeHtml(symbol)}</div>`;
         }
-        toHtml += approvalAddressHtml(toAddr);
+        toHtml += approvalAddressHtml(toAddr, approvedTx.chainId);
         $("approve-tx-to").innerHTML = toHtml;
     } else {
         $("approve-tx-to").innerHTML = escapeHtml(CONTRACT_CREATION_TEXT);
@@ -388,7 +400,10 @@ function showTxApproval(details) {
                 if (d.isToken) {
                     detailsHtml += `<div class="font-bold">${escapeHtml(tokenLabel(d.address, approvedTx.chainId) || "Unknown token")}</div>`;
                 }
-                detailsHtml += approvalAddressHtml(d.address);
+                detailsHtml += approvalAddressHtml(
+                    d.address,
+                    approvedTx.chainId,
+                );
             } else {
                 detailsHtml += `<div class="font-bold">${escapeHtml(d.value)}</div>`;
             }
diff --git a/tests/approvalTokenNetwork.test.js b/tests/approvalTokenNetwork.test.js
index 20ed1dc..914433f 100644
--- a/tests/approvalTokenNetwork.test.js
+++ b/tests/approvalTokenNetwork.test.js
@@ -1,11 +1,16 @@
 // The approval screen for a site's Sepolia token transfer while Ethereum
-// Mainnet is active (https://git.eeqj.de/sneak/AutistMask/issues/629).
+// Mainnet is active.
 //
 // The screen named the token, and scaled its amount, from the active network's
 // tracked tokens and balances, so a token the wallet tracks on Sepolia read as
 // an unknown token with its amount in base units, and the screens after it
-// labelled the amount `?`. It now uses what the wallet knows of the tokens on
-// the network the transaction is for.
+// labelled the amount `?` (https://git.eeqj.de/sneak/AutistMask/issues/629).
+// It now uses what the wallet knows of the tokens on the network the
+// transaction is for.
+//
+// Its address links opened the active network's explorer
+// (https://git.eeqj.de/sneak/AutistMask/issues/631). They now open the
+// explorer of the network the transaction is for.
 //
 // Driven through the real approval screen, password and Confirm included,
 // against a minimal DOM stub in the shape tests/swapStatusAmount.test.js uses.
@@ -107,10 +112,13 @@ function decodedLine(label) {
 }
 
 // Open the approval screen, with Ethereum Mainnet active and FROM holding
-// `tokenBalances` there, for the site's Sepolia transaction sending
-// TRANSFER_DATA to the token. Confirm answers the signed transaction with a
-// failure, which leads to the error screen.
-async function showSepoliaTransfer(tokenBalances = []) {
+// `tokenBalances` there, for the site's transaction sending TRANSFER_DATA to
+// the token, on Sepolia unless `chainId` names another chain. Confirm answers
+// the signed transaction with a failure, which leads to the error screen.
+async function showTokenTransfer(
+    tokenBalances = [],
+    chainId = NETWORKS.sepolia.chainId,
+) {
     globalThis.document = makeDocument();
     globalThis.window = { location: { search: "" }, close: () => {} };
     globalThis.chrome.runtime = {
@@ -131,7 +139,7 @@ async function showSepoliaTransfer(tokenBalances = []) {
                 approvedTx: {
                     type: 2,
                     from: FROM,
-                    chainId: NETWORKS.sepolia.chainId,
+                    chainId,
                     nonce: "0x7",
                     gasLimit: "0x30d40",
                     maxPriorityFeePerGas: "0x3b9aca00",
@@ -183,7 +191,7 @@ describe("a token tracked on Sepolia only", () => {
     });
 
     test("is named on the Contract line and the decoded Token line, with its amount at its scale", async () => {
-        await showSepoliaTransfer();
+        await showTokenTransfer();
         expect(node("approve-tx-to").innerHTML).toContain(
             '<div class="font-bold mb-1">TDOL</div>',
         );
@@ -196,7 +204,7 @@ describe("a token tracked on Sepolia only", () => {
     });
 
     test("labels the amount on the error screen that follows", async () => {
-        await showSepoliaTransfer();
+        await showTokenTransfer();
         await confirm();
         expect(state.currentView).toBe("error-tx");
         expect(node("error-tx-summary").textContent).toBe("1234.5000 TDOL");
@@ -207,7 +215,7 @@ describe("a token tracked on Sepolia only", () => {
 // tracks and holds there names nothing on Sepolia.
 test("a token tracked and held on mainnet only is not named, and its amount is in base units", async () => {
     state.trackedTokens = [{ address: TOKEN, symbol: "MDOL", decimals: 18 }];
-    await showSepoliaTransfer([
+    await showTokenTransfer([
         { address: TOKEN, symbol: "MDOL", decimals: 18, balance: "1.0" },
     ]);
     expect(node("approve-tx-to").innerHTML).not.toContain("MDOL");
@@ -218,3 +226,45 @@ test("a token tracked and held on mainnet only is not named, and its amount is i
         '<div class="font-bold">1234500000 base units (decimals unknown)</div>',
     );
 });
+
+// The From and Contract lines, and the decoded Token and Recipient lines.
+test("every address links to the Sepolia explorer", async () => {
+    await showTokenTransfer();
+    const sepolia = NETWORKS.sepolia.explorerUrl;
+    expect(node("approve-tx-from").innerHTML).toContain(
+        `href="${sepolia}/address/${FROM}"`,
+    );
+    expect(node("approve-tx-to").innerHTML).toContain(
+        `href="${sepolia}/address/${TOKEN}"`,
+    );
+    expect(decodedLine("Token")).toContain(
+        `href="${sepolia}/address/${TOKEN}"`,
+    );
+    expect(decodedLine("Recipient")).toContain(
+        `href="${sepolia}/address/${RECIPIENT}"`,
+    );
+    for (const id of [
+        "approve-tx-from",
+        "approve-tx-to",
+        "approve-tx-decoded-details",
+    ]) {
+        expect(node(id).innerHTML).not.toContain(NETWORKS.mainnet.explorerUrl);
+    }
+});
+
+// Chain id 1337 names no network here, so it has no explorer to link to.
+test("a transaction on a chain id that names no network is shown with no address links", async () => {
+    await showTokenTransfer([], "0x539");
+    expect(state.currentView).toBe("approve-tx");
+    expect(node("approve-tx-network").textContent).toBe(
+        "Unknown network (chain id 1337)",
+    );
+    expect(node("approve-tx-from").innerHTML).toContain(FROM);
+    for (const id of [
+        "approve-tx-from",
+        "approve-tx-to",
+        "approve-tx-decoded-details",
+    ]) {
+        expect(node(id).innerHTML).not.toContain("href=");
+    }
+});
diff --git a/tests/walletDefects.test.js b/tests/walletDefects.test.js
index d5e9ea5..fe1c389 100644
--- a/tests/walletDefects.test.js
+++ b/tests/walletDefects.test.js
@@ -475,7 +475,7 @@ describe("every way to a signature or the private key refuses a defective wallet
                 to: RECIPIENT,
                 value: "0x0",
                 data: "0x",
-                chainId: 1,
+                chainId: "0x1",
                 nonce: 0,
                 gasLimit: "21000",
                 maxFeePerGas: "1000000000",