Firefox 153 previews 'new' Containers a user traced back to 2017

Mozilla brings container tabs into Firefox itself, no extension required

On July 21, Mozilla announced that Firefox 153 folds container tabs into the browser itself as a first-party preview, not an add-on. The pitch: open different tabs in isolated containers, each with its own cookie jar, so a work Google account, a personal one, a bank, and Amazon never share cookies or ad-tracking data. Containers get custom names, colors, and icons, and are managed straight from Firefox's Settings, reached by right-clicking a tab or long-pressing the new-tab button.

That isolation used to live only in Mozilla's own Multi-Account Containers extension, and the post is upfront that switching isn't a clean break yet. It states: "Installing the Multi-Account Containers extension developed by Mozilla provides a few benefits on top of the native container functionality like site-specific container assignments, syncing across devices, and integration with Mozilla VPN or your own proxy." In practice: syncing containers across your laptop and desktop, and auto-opening a given domain in a given container, both still require the add-on. Mozilla says it is collecting feedback on a Connect thread before deciding what ships next.

A reader rebuilt the same feature in a nine-year-old snapshot

Not everyone in the thread read "preview" as a launch. One reader skipped the comments and went to the Wayback Machine instead.

"I just created a new profile in Firefox 140 ESR, started it in safe mode (which disables extensions), enabled 'privacy.userContext.enabled' in about:config - and there you go, native containers accessible from File -> New Container Tab. … The Containers feature is already a 'native, first-party feature' in older versions of Firefox." — a reader who reproduced the feature from scratch, extensions fully disabled

Their evidence: a 2017 snapshot of Mozilla's own developer documentation already showing the container UI, and a 2023 support-page snapshot flatly calling containers "a basic built-in feature." Nothing in the July post explains what actually changes for someone who flipped that config flag years ago, or whether the flag is finally becoming Firefox's default.

Containers or profiles: the thread picks a side

Firefox also shipped browser profiles recently, which reopened a separate argument in the comments: which isolation tool a privacy-conscious user should actually reach for.

"I use profiles for this… For me I really think profiles are better since the boundaries are harder - there's no worry about accidentally hitting the 'log in with Google' button and clearly identifying myself to a site or similar… But I feel like containers may be too squishy." — a sysadmin who prefers profiles for the same isolation job

For power users already sold on containers, the appeal is finer-grained than switching a whole profile:

"For me the big use case is having different Google accounts active in one window. Work and private… Using different colors for each makes it easy to tell apart the tabs… I also keep my bank's website in its own container just on principle." — a Berlin-based backend developer and startup CTO

The third extension feature Mozilla has folded in-house this year

Containers joins a built-in color picker and native PDF editing as recent extension-to-core moves, a pattern one reader tallied directly in the thread:

"For a long time, with relatively limited (compared to Google and Apple) development resources, they focused on minimizing upkeep and technical debt… Now I'm seeing geek and power user favorites like a built-in color picker, PDF editing features, and now multi-account containers moved into the browser. What changed?" — a reader cataloguing Mozilla's last three extension-to-core moves

If Mozilla really is re-absorbing its most-used extensions rather than just previewing one, container users have a concrete test ahead: whether device sync and per-site auto-assignment, the two pieces still locked to the add-on, land in Firefox core before the extension itself becomes redundant.