Mozilla Thimble

» see thimble.mozilla.org as it lived, on the wayback machine

~ the obituary ~

Mozilla put Thimble on the web on 18 June 2012 with a layout anyone could read in a second. Your HTML sat in the left half of the browser window and the page it produced sat in the right half, redrawing itself as you typed. Break a tag and the right side broke with it, in front of you, with a hint in the margin telling you which bracket you had lost. Press publish and the thing got a real URL that a real person could open.

It came out of Webmaker, the education side of the Mozilla Foundation, back when the foundation still treated teaching people to make a web page as being as much its job as shipping a browser. Thimble projects were meant to be taken apart. Every published page could be remixed, which meant opening somebody else's markup in your own editor and changing it until it was yours, and a lot of teachers used exactly that as the first hour of a class.

In 2015 Mozilla rebuilt the whole thing on Bramble, a fork of Adobe's open source Brackets editor, and the toy grew up. The new Thimble had a file tree and a preview that understood a whole small site rather than one document. By the end it was holding over 1.4 million projects.

I was about a decade past needing it. By 2012 web pages were work, and the lesson Thimble taught, that everything on a screen is text somebody typed and you are allowed to edit that text, is a thing I had absorbed slowly and unofficially years earlier, in the dial-up window when looking at a page's source was the only tutorial available. Thimble is that discovery with the lid taken off and a classroom built around it. A better version of how I learned, arriving for people fifteen years younger than me.

~ the case file ~

~ the editor inside the editor ~

The 2015 rewrite is the part with a joke in it. Thimble's engine was a fork of Brackets, the open source code editor Adobe had built and given away, so Mozilla's teaching tool was running on Adobe's developer tool. Adobe discontinued Brackets in September 2021, almost two years after Mozilla had already switched Thimble off. Both editors are now read-only history on GitHub, and the repository for Thimble carries a one-line note at the top telling you to go use Glitch instead.

~ the year of notice ~

On 18 December 2018 Mozilla and Glitch announced the wind-down together, which gave everybody a full twelve months. That is an unusually long runway for a free product, and the reason was school calendars: Thimble was in courses, and a shutdown dropped mid-semester takes live assignments down with it.

The last day was 16 December 2019. Anybody could keep using Thimble without an account until that date, and anybody with an account was told to move their work to Glitch before it. Mozilla's own explanation was that Thimble had been in maintenance mode for some time while the organization refocused its resources elsewhere.

~ where the projects went ~

Glitch took the 1.4 million projects and committed to keeping them online, and for a while that held. Fastly bought Glitch in 2022 and said nothing would change about your apps. Then on 8 July 2025 Glitch ended project hosting altogether, with dashboards staying open until the end of that year so people could download their code. Today glitch.com forwards to the Glitch blog.

Thimble's own address stopped answering some time after the shutdown. For a stretch it forwarded to a Mozilla Foundation page filed under the word artifacts, which is where the foundation keeps its dead work, and that page is still standing while the product it describes is not.

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