Tor Browser 15.0: What’s New, What’s Changing, and What to Watch

Quick take

Tor Browser 15.0 is now available from the official download page and distribution directory. This is the first stable build on Firefox ESR 140, which rolls in a year’s worth of upstream browser changes. As part of the upgrade, Tor’s engineers completed their annual ESR transition audit—reviewing roughly 200 Firefox changes for privacy or security regressions—and published their findings in the tor-browser-spec repository.

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What’s new (Desktop)

Vertical tabs & sidebar goodies. You can stack open and pinned tabs in a vertical sidebar instead of across the top. When the sidebar is open, Bookmarks are a click away.

Tab groups. Corral tab chaos by grouping related tabs, naming the group, and color-coding it. Groups collapse/expand so you can keep focus.

Address bar refresh. You’ll notice a unified search button in the URL bar: switch engines on the fly, search bookmarks or tabs, and trigger quick actions from the same menu.

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What’s new (Android)

Screen lock for tabs. Enable Settings → Tabs → Screen lock to auto-lock your open tabs whenever you switch away from the app without closing it. When you return, unlock with your device method (fingerprint, face, or passcode).

Your Tor session still clears when you quit the app. Screen lock is about protecting an already-open session if someone briefly handles your unlocked phone.

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What’s changing (heads-up for Tor 16.0)

Mozilla plans to raise the floor for Android support to Android 8.0+ and to drop x86 support on Android and Linux. Tor Browser 15.0 continues to support Android 5–7 and x86 for now, but 15.x will be the last major line to do so. Security updates will continue until Tor Browser 16.0 ships (mid-next year), when the new minimums take effect.

Why the change? Maintaining very old platforms introduces instability and limits modern defenses. x86 on Android has also been a packaging headache due to the 100 MB Google Play cap; keeping within that limit has meant compromises (e.g., some users missing the Conjure pluggable transport).

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WebAssembly control moves to NoScript

WebAssembly (Wasm) improves web-app performance but also expands attack surface. Tor’s Safer and Safest levels have long disabled Wasm. Previously, Tor flipped the global javascript.options.wasm preference; however, parts of Firefox’s PDF reader now use Wasm (since 128–140), so Tor shifted Wasm control to NoScript:

• Privileged pages (like the built-in PDF viewer) can use Wasm so they work correctly.
• Regular sites still have Wasm blocked at Safer/Safest via NoScript.

If you manually set javascript.options.wasm=false while on Standard, Tor will label your level Custom. That may make your fingerprint more unique. To stay within Tor’s standard fingerprint, either revert that pref to true or let NoScript handle it by using the built-in security levels instead of tweaking about:config.

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Known issues in 15.0

Desktop

• With the sidebar visible (e.g., vertical tabs), the window can visibly resize at launch.
• Letterboxing may appear due to those size variations. Anti-fingerprinting is still active; the default window size just isn’t ideal yet.

A fix is in progress (see issue tor-browser#44096).

Android

• On older Android versions, pages may fail to load after updating. Fix: clear the app cache:
  Settings → Apps → Tor Browser → Storage & cache → Clear cache.

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Get involved

Spotted a bug or have a suggestion? File feedback in the Tor issue tracker. If you’d like to contribute code, check out the Tor Project’s new contributor guide—and consider donating (matching in effect through Dec 31, 2025).

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OnionSpace tips for 15.0

• Prefer Safer or Safest if you don’t need advanced web features.
• Keep Tor updated; don’t install extra add-ons.
• Use tab groups to isolate research threads within a single session, then close Tor to wipe state clean.