What is "net.thunderbird" integration in 152.0?

Which version of Windows?

Windows 10. What is net.thunderbird? Do I want it integrated?

I reviewed the Windows 10 info, and it appears all supported for me, if that helps.

I saw that too at, the update to v152.0. Using Win11 Pro 25H2 build 26200.8655. Appears 'Always check to see if Thunderbird is the default mail client on startup' had become enabled - not by me. It didn't happen at the Beta update to 153.

1. What is net.thunderbird?
2. Do I want it integrated?

Perhaps there are other issues to be addressed, but for now I am required by Thunderbird to answer the pop-up. Unfortunately, I do not know how to answer without those simple answers that I cannot seem to find in Help or in searches. Assistance is appreciated.

# What is net.thunderbird?

1. Do I want it integrated?

Perhaps there are other issues to be addressed, but for now I am required by Thunderbird to answer the pop-up. Unfortunately, I do not know how to answer without those simple answers that I cannot seem to find in Help or in searches. Assistance is appreciated.

I'm not exactly sure what Custom Thunderbird links are, but my guess is that they would open in the Thunderbird browser vs. a regular browser. You should enable that, along with 'Email' and any of the others you want, and enable 'Always perform this check...' too Then press the 'Set as Default' button and restart TB. At that point, you shouldn't get the popup any more.

I saw that too at, the update to v152.0. Using Win11 Pro 25H2 build 26200.8655. Appears 'Always check to see if Thunderbird is the default mail client on startup' had become enabled - not by me. It didn't happen at the Beta update to 153.

Actually, that option had become disabled. Which makes the question of 'why the popup?' even more interesting.

I'm not exactly sure what Custom Thunderbird links are, but my guess is that they would open in the Thunderbird browser vs. a regular browser.

Thanks for the shot at it. If it opens a web link, I would want to view it in my regular browser with all the browser features I use — unless there is a special purpose or use for net.thunderbird? Without more info, I will have to default to not selecting it, also hoping I can reverse that decision in the future when I know something about it.

I would still appreciate any specific info on what it is? Any way to get info from Mozilla about it?

FYI, opting out of net.thunderbird was not acceptable, and I had to allow it in order to stop the pop-up on every access. While we shrug and figure stuff like this must be "OK", it's a bit disturbing when no info is offered to the user if it is not really an option and must be accepted. If i find more info or effects from it, I will follow-up here. Thanks to all that replied.

you might want to file a bug report about your inability to opt out of having that option included in the check. Personally I see mine as unchecked when I select check now in the integration in settings.

Good idea, as a check of system integration on mine (if I'm in the correct location) shows no mention or option:

Click the check now button and make sure the new option is not selected. I only have the daily developer build to play with, but it was not selected by default when I checked it. so perhaps there is still some work happening in the background regarding defaults.

PS developer build is 154.0a1 (2026-06-21)

Good idea, as a check of system integration on mine (if I'm in the correct location) shows no mention or option:

It's not supposed to be there - only when you 'Check now'.