We implemented this in the Daily build of the desktop app last year, using a staging environment for Firefox Sync. But Firefox Sync is called Firefox Sync because it’s built for Firefox. Thunderbird profiles, in comparison, have a lot more data points. This meant we had to build something completely different. As we started to spin up Thunderbird Pro, we decided it made more sense to have a Thunderbird account that would manage everything, including Sync. Unfortunately, this meant a lot of delays. So Sync is still on our radar, and we hope to have it next year, barring further complications. Source: https://blog.thunderbird.net/2025/09/state-of-the-thunder-mo...
In other words, it was more work to adapt Firefox Sync than they thought at the beginning. It's still actively developed so finger crossed it's coming soon.
Exactly this. Plus, I rarely have over 20 tabs and even when I'm close to that number I mainly use the 10 first ones. Vertical tabs is a cool feature but both modes are useful depending your needs.
Mozilla Foundation is a non-profit but Mozilla Corporation which develop Firefox is a for-profit entity.
There are other subsidiaries under the foundation umbrella like Mozilla.ai and MZLA/Thunderbird. This isn't something uncommon for large entity and there are many advantages. For example, it gives more freedom in term of decision making and spending to projects that aren't targeting the exact same consumer segment. Think about Thunderbird. Under Mozilla Corporation, it was always in the shadow of Firefox. Now, it's striving as an independent project.
It's easier to do small releases often. You have less chances to break multiple parts of the application. You also don't end up in a cycle of "Wait! I'll add just one more thing" which is very common with projects tend to less often.
In other words, it was more work to adapt Firefox Sync than they thought at the beginning. It's still actively developed so finger crossed it's coming soon.