Tbird version is 115.6.0 for Debian.

Try using the "find more providers" under the list of installed providers. Once you do that, click the add to Thunderbird from dropbox Then click on the add drop box link that has appeared above the find more providers. Then use the link that appears on the right of the providers list to sign into dropbox. Then copy the link you are presented with and paste it into the authorization code window in Thunderbird. If you got it right the message changes to "you're good to go"

As the Dropbox web component uses oauth2.0 authorization, I would guess you need to have cookies enabled in Thunderbird's settings. That is the default for normal versions, but those from Linux maintainers often vary from standard builds based on the ideology of the maintainer. So I suggest you check.

Thanks Matt but it doesn't work. I click the link and it hangs, as I described. Cookies is enabled.

BTW I can manually upload to dropbox and cut and paste links in emails which all works fine.

I just completed those steps after I read your post. So I will guess this is another of those Linux things, because I demonstrated to myself that it works in Windows 11.

When you say cookies are enabled, that is in Thunderbird, not somewhere else.

God knows, maybe it is a Linux thing. Yes, cookies enabled in Tbird.

It "might" be a firewall issue, as Thunderbird usually hangs while it waits for a response that never comes

But it might also be a permissions issue. The process is writing to the profile folder and I have no idea if the process runs with current users permissions or something else.

Dunno. I tried installing via a file, but same thing, the popup box displays and then hangs.

BTW, it seems this applies to any addon, not just dropbox -- I can't add anything. Reinstall didn't help.

Matt, should I resubmit this question? Seems it has nothing to do with dropbox, it's *all* add-ons.

See https://bugzilla.mozilla.org/show_bug.cgi?id=1829370

Ok so this is a known bug then. I don't suppose there's an ETA for a fix? Seems that complete breakage of addons would merit speedy action. I'd be happy to serve as a tester if something is offered.

Matt, should I resubmit this question? Seems it has nothing to do with dropbox, it's *all* add-ons.

Nope.

You might say where you got your copy of Thunderbird from. The flatpak one appears to have had some issues around permissions and Linux being the diverse animal it is, every copy your get from different sources is usually actually a different program you install.

I resubmitted the issue anyway and it seems this is a known bug with the Linux version. (Debian in my case) I'd have thought a complete failure of the add-on mechanism would warrant immediate attention but it seems not. I always thought that Mozzila was going to be centered on Linux, with the Windows version an afterthought, but it seems that's backwards.