User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0

Steps to reproduce:

1. Click on Thunderbird v. 79.0a1.
2. Wait ...

Actual results:

Program screen finally loads after about 2.5 minutes. The loading time is reduced significantly (less than 30 seconds) when Windows Defender (Windows 10) real time protection is turned off. During the 2.5 minutes, the activity of the "Antimalware Service Executable" rises to about 30% CPU.

Expected results:

Program should have loaded quickly, as previous versions were.

The core question likely is, why is defender doing things it shouldn't.

Is it doing something it should not Wayne? I would guess 79 might well be "unknown" software in the Microsoft database, at least early builds.

(In reply to Matt from comment #2)

... 79 might well be "unknown" software in the Microsoft database, at least early builds.

Yes, this can happen.

It is also possible this is made worse by bug 1637668 which landed in 78. Let's assume so, and see what happens after bug 1652279 is fixed

carodri2,
Can you check this candidate build and tell us if the situation improves?
https://archive.mozilla.org/pub/thunderbird/candidates/79.0b3-candidates/build1/

Yes, this candidate release 79b3 opens much much quicker! It only took like 5 seconds.

Now if we can put the same sauce into Daily, it would be perfect.

Correction: 5 seconds with a blank profile. With my profile loaded, it took about 30 seconds, which is much better than before.

The correction comes from bug 1652279 whose patch should be in this morning's daily build.