A while back, I stumbled onto something that turned into a rewarding side-project at Mozilla.
Firefox ships with a built-in spellchecker, but it only activates if a dictionary for your language is bundled with the browser. Coverage had grown organically over the years — driven largely by localizers and community members adding support for their own languages. Dictionary work was actually very active in the early years of the Mozilla project, but like many things in a large open-source codebase with a lot to manage, it had quietly received less attention over time, for no particularly good reason. So I decided to change that.
Taking stock
I put together a full inventory dashboard of every third-party dictionary shipped in Firefox Desktop, cataloguing sources, upstream health, and — critically — licensing.
Licensing turns out to be the main bottleneck. Firefox is open-source software, so any dictionary we ship has to carry a licence compatible with the Mozilla codebase. Some excellent dictionaries exist for languages Firefox supports, but their licences don't allow direct inclusion. In those cases, the dictionary can still reach users — but only as a Firefox extension they have to find and install manually, rather than something that just works out of the box.
The goal of the inventory wasn't to point fingers at anything. It was to make the full picture visible, so that anyone who wanted to help would know exactly where to start.
Plugging into the community
Once the inventory existed, the work was really about connecting the right people. Mozilla's localizer community already had the expertise and motivation — what was sometimes missing was a clear entry point. I took care of all the patches myself, so that localizers wouldn't have to deal with the technical side of things. This work was done in coordination with Mozilla's Localization drivers team, who own the dictionary infrastructure and reviewed and merged the changes.
The results
We expanded the number of locales shipping with a built-in dictionary from 30 to 41. This shipped last week with Firefox 151.0.3, and these improvements also benefit Thunderbird users, since both applications share the same dictionary infrastructure.
New dictionaries added: Croatian, English (UK), Georgian, Persian, Slovenian, Tajik, Tamil, Tibetan, Turkish, Welsh, and Xhosa.
Updated dictionaries: Bulgarian, Danish, French, Hungarian, Indonesian, Latvian, Polish, Romansh, and Swedish.
Stirring the pot
Part of the reason for doing this work publicly — building the inventory, filing the bugs, making the gaps visible — was to give people with the right expertise a reason to step in themselves. That's exactly what happened.
For Turkish and Russian, the existing open-source Hunspell dictionaries had become outdated — vocabulary and linguistic rules that hadn't kept pace with how the languages are actually used today. Selim (our Turkish l10n lead) and Valentin (our Russian l10n lead) each decided to take matters into their own hands.
Selim forked the TDD Turkish dictionary and updated it with modern vocabulary, better circumflex support, and performance improvements — the result is hunspell-tr-moz, now shipping in Firefox 151.0.3. Valentin built a new modern Russian dictionary from scratch, ru-spelling-dictionary, released under MPL-2.0. It's currently available as a Firefox extension — if you use Russian, Valentin would appreciate feedback on the quality before it's integrated directly into Firefox.
Both projects are public and open-source.
What's still in the pipeline
The licence question is also quietly resolving itself for a couple more locales. The maintainers of the Kabyle and Asturian dictionaries have agreed to relicense their work to allow direct inclusion in Firefox. Once that's done, those communities will join the list too.
There are still gaps in the inventory. Some are licence issues that may resolve over time. But for many of the remaining locales, the honest answer is that we simply haven't looked hard enough yet. Dictionaries are often individual passion projects or work coming out of linguistics circles — they exist, but finding them takes investigation. If you know of a dictionary for a language Firefox doesn't currently support, that's exactly the kind of lead worth following up on.
An open invitation
Mozilla is still a place where a motivated contributor can find a corner of the project, do meaningful work, and have a real impact — without needing to be a browser engineer or a Mozilla insider.
The inventory dashboard is public. If you're a localizer, a linguist, or a dictionary maintainer and you want to help bring spellchecking to more Firefox users, the gaps are clearly documented. And if you maintain a dictionary that could be included but licensing is an obstacle, that's a conversation worth having.
See you in May 2027 for the next update.
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