Dev tools · September 11, 2023
Firefox addon to quarantine a tab to use offline with private data
Introducing QuaranTab: Companion extension to quarantine tabs so you can safely use them offline with private data I find myself wanting to use online format parsers to quickly decode that production JWT or decode a base64 Authorization header but cannot trust these websites to not leak my information. I thought to myself if only I could cut-off network access to this site, use it offline, and then throw away all browsing data. So I created an extension just for that. It uses Firefox contextual identities API (Containers) to isolate browsing data and inter-tab communication. Once the site is…
In plain words
QuaranTab is a Firefox extension that lets developers safely use online tools with sensitive data by isolating them offline. It quarantines websites in separate containers, blocks network access after loading, and automatically deletes all browsing data when done. The tool is designed for tasks like decoding JWTs, parsing authorization headers, hashing passwords, and converting data formats without risking information leakage to untrusted services.
written from the facts on this page · September 2026
From the sources
In the maker’s words, at launch
Introducing QuaranTab: Companion extension to quarantine tabs so you can safely use them offline with private data I find myself wanting to use online format parsers to quickly decode that production JWT or decode a base64 Authorization header but cannot trust these websites to not leak my information. I thought to myself if only I could cut-off network access to this site, use it offline, and then throw away all browsing data. So I created an extension just for that. It uses Firefox contextual identities API (Containers) to isolate browsing data and inter-tab communication. Once the site is fully loaded, I then inject bogus proxy settings for any requests leaving that container to effectively cut-off network access. And once I'm done, I simply delete the Container. Use Cases: * Parse a live JWT token * Convert a Base64 Authorization header * Hash a password * Parse a Protobuf message * Submit my name and birthdate to estimate my date of death Check out the MIT source code on GitHub [1] and install QuaranTab from the Firefox store [2]. If anyone is interested in a discussion, I'd love to chat about: 1. Any ideas on how we could implement this in Chromium? Using private window as a "Container"? 2. Can you come up with an exploit? I posted a 100usd bug bounty [3] if you find one! 3. Is there any way to prove an extension in the store was built from source in GitHub? I am imagining some kind of third-party escrow service managing the Firefox store account and building from specific public git repository. 1. https://github.com/matusfaro/quarantab 2. https://addons.mozilla.org/en-US/firefox/addon/quarantab/ 3. https://github.com/matusfaro/quarantab#bug-bounty
Does the same job
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