Haven't seen this distorted before, maybe an upstream regression.

STR

1. install Thunderbird Setup 87.0b1.2021-03-01.beta.DE (with other beta versions present I guess) on a Win10 desktop environment with two screens (forming one desktop).

Actual (see screenshot)

• "This installation of Thunderbird Daily has a new profile..." alert is unreadable because it extends across both screens whilst not even beeing centered, so left side of alert is hidden to the left, outside screen 1.

Expected

• sanity-check size, position, and visibility of this alert with multiple screens
• don't extend the alert across more than the current screen
• limit alert width to something sane so that it doesn't end up as one long line.

https://searchfox.org/comm-central/rev/7dcededfeafb2a0c052c7329cc7cfdcbc7f1111c/mail/base/content/newInstall.xhtml#22

Bug 1590884 comment 22 may be relevant. But that's for 88. Something must have changed in the 87 cycle as well, as there was another case too where <description> was changed.

We may want to just change it to html:p instead of xul:description

The part about screens is probably not relevant, it just makes the width even more obscene.

NOTE: for testing this feature, keep track of profiles.ini, and create an create a new profile. Now from profiles.ini, delete the entry for the profile that the install you just run created. Start again (but do not specify a profile!)