diff --git a/core/hosted.js b/core/hosted.js
index cb0f12a..628b692 100644
--- a/core/hosted.js
+++ b/core/hosted.js
@@ -124,7 +124,8 @@ export function plainCovered(rules, bucket, key) {
 }
 
 const MIME = {
-  html: 'text/html', htm: 'text/html', txt: 'text/plain', md: 'text/markdown', css: 'text/css', js: 'text/javascript',
+  html: 'text/html', htm: 'text/html', txt: 'text/plain', md: 'text/markdown', css: 'text/css', js: 'text/javascript', mjs: 'text/javascript',
+  wasm: 'application/wasm', woff: 'font/woff', woff2: 'font/woff2', ttf: 'font/ttf', otf: 'font/otf', webmanifest: 'application/manifest+json',
   json: 'application/json', xml: 'application/xml', csv: 'text/csv', pdf: 'application/pdf', zip: 'application/zip',
   png: 'image/png', jpg: 'image/jpeg', jpeg: 'image/jpeg', gif: 'image/gif', webp: 'image/webp', svg: 'image/svg+xml', avif: 'image/avif', ico: 'image/x-icon',
   mp3: 'audio/mpeg', ogg: 'audio/ogg', oga: 'audio/ogg', wav: 'audio/wav', flac: 'audio/flac', m4a: 'audio/mp4', opus: 'audio/opus',
diff --git a/core/server.js b/core/server.js
index 7fb7709..c38494d 100644
--- a/core/server.js
+++ b/core/server.js
@@ -26,6 +26,7 @@ import { readPrefs, writePrefs } from './prefs.js';
 import { createAutoFlush, clampMinutes, DEFAULT_MINUTES } from './autoflush.js';
 import { installHosted } from './hosted-routes.js';
 import { accountInfo, readConnection, fingerprint } from './sia-account.js';
+import { guessType } from './hosted.js';
 
 const HERE = path.dirname(fileURLToPath(import.meta.url));
 const UI_DIR = path.join(HERE, '..', 'ui');
@@ -418,6 +419,68 @@ export async function createPithos(opts = {}) {
     return { prefix };
   });
   // Small text files for the viewer (first 512 KiB).
+  // HTML opened as a page. A ticket covers the folder the page sits in, so
+  // its relative CSS, images, scripts and links resolve; it lasts an hour from
+  // the last use (12 hours at most). See servePage for the sandbox.
+  const pages = new Map(); // id -> { user, bucket, prefix, exp, until }
+  route('POST', '/api/s3/:user/buckets/:bucket/page', async (req, url, p) => {
+    const { key } = await jsonBody(req);
+    if (typeof key !== 'string' || !/\.html?$/i.test(key)) throw new HttpError(400, 'only .html files open as pages');
+    const now = Date.now();
+    for (const [k, v] of pages) if (v.exp < now) pages.delete(k);
+    if (pages.size >= 200) throw new HttpError(429, 'too many pages open; close some and try again');
+    const cut = key.lastIndexOf('/') + 1;
+    const id = crypto.randomBytes(24).toString('base64url');
+    pages.set(id, { user: p.user, bucket: p.bucket, prefix: key.slice(0, cut), exp: now + 60 * 60_000, until: now + 12 * 3600_000 });
+    return { path: `/page/${id}/${key.slice(cut).split('/').map(encodeURIComponent).join('/')}` };
+  });
+
+  // The page and its neighbours. The sandbox CSP (no allow-same-origin) gives
+  // the page an opaque origin: its scripts run, but requests they make to this
+  // server are cross-site, so they carry no session cookie and cannot pass
+  // the x-pithos check. They can only read files the ticket covers.
+  // The page loads whatever it links to (it is the user's own site); the
+  // sandbox is the boundary, not a source list.
+  const PAGE_CSP = "sandbox allow-scripts allow-forms allow-popups allow-modals allow-downloads; frame-ancestors 'self'";
+  async function servePage(req, res, id, rest) {
+    const t = pages.get(id);
+    const now = Date.now();
+    if (!t || t.exp < now) { res.writeHead(410, { 'content-type': 'text/plain; charset=utf-8' }); return res.end('This page link has expired. Open the file from Pithos again.'); }
+    t.exp = Math.min(now + 60 * 60_000, t.until);
+    let segs;
+    try { segs = rest.split('/').map((x) => decodeURIComponent(x)); } catch { res.writeHead(400); return res.end('bad path'); }
+    if (!segs.length || segs[segs.length - 1] === '') segs[segs.length ? segs.length - 1 : 0] = 'index.html';
+    // An encoded slash would make one "segment" span folders (..%2F..).
+    if (segs.some((x) => !x || x === '.' || x === '..' || /[/\\]/.test(x))) { res.writeHead(400); return res.end('bad path'); }
+    const key = t.prefix + segs.join('/');
+    const up = await (await s3For(t.user)).getObject(t.bucket, key, { range: req.headers.range });
+    if (up.statusCode >= 300 && up.statusCode !== 304) {
+      up.resume?.();
+      res.writeHead(up.statusCode === 416 ? 416 : 404, { 'content-type': 'text/plain; charset=utf-8', 'content-security-policy': PAGE_CSP });
+      return res.end(up.statusCode === 416 ? 'range not satisfiable' : 'not found');
+    }
+    // The extension decides for web files: S3 clients often store HTML, CSS or
+    // scripts as octet-stream (or anything), and a page must load them as such.
+    const guessed = guessType(key);
+    const stored = up.headers['content-type'];
+    let type = guessed !== 'application/octet-stream' ? guessed : (stored || guessed);
+    if (/^text\/|javascript|json|xml|svg/i.test(type) && !/charset=/i.test(type)) type += '; charset=utf-8';
+    const headers = {
+      'content-type': type,
+      'content-security-policy': PAGE_CSP,
+      'x-content-type-options': 'nosniff',
+      'cache-control': 'no-store',
+      // The sandboxed page is cross-origin even to itself; its scripts may read
+      // the files its ticket covers (the ticket in the URL is the secret).
+      'access-control-allow-origin': '*',
+    };
+    for (const h of ['content-length', 'content-range', 'accept-ranges', 'last-modified', 'etag']) if (up.headers[h]) headers[h] = up.headers[h];
+    res.writeHead(up.statusCode, headers);
+    if (req.method === 'HEAD') { up.resume?.(); return res.end(); }
+    up.on('error', () => res.destroy());
+    up.pipe(res);
+  }
+
   route('GET', '/api/s3/:user/buckets/:bucket/text', async (req, url, p) => {
     const up = await (await s3For(p.user)).getObject(p.bucket, requireKey(url), { range: 'bytes=0-524287' });
     const body = await readBody(up);
@@ -536,8 +599,18 @@ export async function createPithos(opts = {}) {
       url = new URL(t.path, url);
       viaTicket = true;
     }
-    res.setHeader('x-frame-options', 'DENY');
     res.setHeader('referrer-policy', 'no-referrer');
+    const page = /^\/page\/([A-Za-z0-9_-]{20,})\/(.*)$/.exec(url.pathname);
+    if (page && (req.method === 'GET' || req.method === 'HEAD')) {
+      // A page may frame its own folder's files; nothing else frames Pithos.
+      res.setHeader('x-frame-options', 'SAMEORIGIN');
+      try { return await servePage(req, res, page[1], page[2]); } catch (e) {
+        if (res.headersSent) return res.destroy();
+        res.writeHead(e instanceof S3Error && e.status < 500 ? e.status : 502, { 'content-type': 'text/plain; charset=utf-8' });
+        return res.end(e.message);
+      }
+    }
+    res.setHeader('x-frame-options', 'DENY');
 
     try {
       // Session bootstrap: ?t=<secret> on any page swaps the secret for a cookie.
diff --git a/desktop/main.cjs b/desktop/main.cjs
index 9e43657..d52ba43 100644
--- a/desktop/main.cjs
+++ b/desktop/main.cjs
@@ -57,7 +57,11 @@ async function start() {
     }
   });
   win.webContents.setWindowOpenHandler(({ url }) => {
-    if (url.startsWith('https://')) shell.openExternal(url);
+    // HTML files opened as pages go to the system browser: the link carries
+    // its own ticket, and the page is sandboxed by the server.
+    const u = new URL(url);
+    if (u.origin === origin && u.pathname.startsWith('/page/')) shell.openExternal(url);
+    else if (url.startsWith('https://')) shell.openExternal(url);
     return { action: 'deny' };
   });
 
diff --git a/theseus/index.js b/theseus/index.js
index 7d15085..16af122 100644
--- a/theseus/index.js
+++ b/theseus/index.js
@@ -182,6 +182,15 @@ module.exports = {
       } });
     }
 
+    // An HTML file from a drive, opened as a page in a new Theseus tab. The
+    // control server sandboxes it (no access to Pithos or the session).
+    api.onMessage("open-page", async ({ path: pagePath } = {}) => {
+      if (!/^\/page\/[A-Za-z0-9_-]{20,}\/[^\s]*$/.test(String(pagePath || ""))) throw new Error("not a page link");
+      const p = await ensureServer();
+      api.openTab(new URL(pagePath, p.url).href);
+      return { ok: true };
+    });
+
     // Full page: Pithos at pithos.sia/<user>/<drive>/… in an ordinary tab.
     // An older Theseus without site routes gets the loopback address.
     api.onMessage("open-in-tab", async ({ path: appPath } = {}) => {
diff --git a/ui/app.js b/ui/app.js
index 0bc01ad..664f4fc 100644
--- a/ui/app.js
+++ b/ui/app.js
@@ -1194,6 +1194,7 @@ function fileKind(key) {
   if (['txt', 'md', 'json', 'csv', 'log', 'xml', 'yml', 'yaml', 'toml', 'ini', 'html', 'htm', 'css', 'js', 'mjs', 'ts', 'py', 'go', 'rs', 'sh', 'sql'].includes(e)) return 'text';
   return null;
 }
+const isHtml = (key) => ['html', 'htm'].includes(EXT(key));
 function suggestBucket(name) {
   let b = String(name || '').toLowerCase().replace(/[^a-z0-9-]+/g, '-').replace(/-+/g, '-').replace(/^-+|-+$/g, '');
   if (b && b.length < 3) b += '-files';
@@ -1453,7 +1454,7 @@ function objectBrowser(head, body, user, bucket, prefix, userSel) {
     const folderName = (f) => f.slice(prefix.length).replace(/\/$/, '');
     const fileName = (o) => o.key.slice(prefix.length);
     const folderMenu = (f) => itemMenu([['Open', () => go(f)], isHosted() && ['Share…', () => folderShareDialog(user, bucket, f)], ['Delete', () => deleteFolder(f), 'danger']]);
-    const fileMenu = (o) => itemMenu([[fileKind(o.key) === 'audio' ? 'Play' : 'Open', () => openViewer(o)], ['Download', () => downloadObject(o.key)], ['Share link…', () => share(o.key)], ['Delete', () => deleteObject(o.key), 'danger']]);
+    const fileMenu = (o) => itemMenu([[fileKind(o.key) === 'audio' ? 'Play' : isHtml(o.key) ? 'Show as text' : 'Open', () => openViewer(o)], isHtml(o.key) && ['Open as page ↗', () => openPage(o.key)], ['Download', () => downloadObject(o.key)], ['Share link…', () => share(o.key)], ['Delete', () => deleteObject(o.key), 'danger']]);
     const more = last?.truncated && h('div', { class: 'row', style: 'justify-content:center;margin-top:12px' }, h('button', { class: 'btn', onclick: () => load(last.nextToken) }, 'Load more'));
     const stop = (e) => e.stopPropagation();
     // Narrow screens: Download and Share as icons beside the ⋯ menu.
@@ -1613,7 +1614,20 @@ function objectBrowser(head, body, user, bucket, prefix, userSel) {
       } else content = h('div', { class: 'empty' }, h('p', {}, 'Pithos cannot show this kind of file.'), h('p', { class: 'small' }, 'Download it to open it on your computer.'));
     } catch (e) { return fail(e); }
     await modal(name, h('div', { class: 'viewer' }, content, h('p', { class: 'small muted', style: 'margin:10px 0 0' }, `${fmtBytes(o.size)} · ${fmtDate(o.modified)}`)),
-      [{ label: 'Share', value: () => { share(o.key); return false; } }, { label: 'Download', value: () => { downloadObject(o.key); return false; } }, { label: 'Close', kind: 'primary', submit: true, result: true }]);
+      [isHtml(o.key) && { label: 'Open as page ↗', value: () => { openPage(o.key); return false; } },
+        { label: 'Share', value: () => { share(o.key); return false; } }, { label: 'Download', value: () => { downloadObject(o.key); return false; } }, { label: 'Close', kind: 'primary', submit: true, result: true }].filter(Boolean));
+  }
+
+  // An HTML file as a web page, in a new tab. The server sandboxes it, so its
+  // scripts run without any access to Pithos; files beside it (CSS, images,
+  // other pages) load as they would from a website.
+  async function openPage(key) {
+    try {
+      const { path } = await api('POST', `${base}/page`, { key });
+      if (bridge) { await bridge.invoke('open-page', { path }); return; }
+      const w = window.open(path, '_blank', 'noopener');
+      if (!w && !/^(desktop)$/.test(state.status?.host)) toast('Allow pop-ups for Pithos to open pages in a new tab', 'error');
+    } catch (e) { fail(e); }
   }
 
   // Music plays in the docked player, on through this folder's other tracks.