`12.0b4` of `.beta` introduces a slower-to-use account switcher.

Checklist

1. I have used the search function to see if someone else has already submitted the same bug report.

2. I will describe the problem with as much detail as possible.

Application

sourcePackage=net.thunderbird.android.beta

Application Version

versionName=12.0b4

Where It Was Installed From

installerPackageName=com.android.vending

#!/usr/bin/env bash
adb shell am start -a android.intent.action.VIEW -d "market://details?id=net.thunderbird.android.beta" && \
adb exec-out uiautomator dump /dev/tty |
    sed 's/></>\n</g' |
    grep -E 'text="(Open|Install|Play|Update)"|content-desc="(Open|Install|Play|Update)"' |
    awk 'match($0,/bounds="\[([0-9]+),([0-9]+)\]\[([0-9]+),([0-9]+)\]/,a){x=(a[1]+a[3])/2;y=(a[2]+a[4])/2;system("adb shell input tap "x" "y)}'

Android Version

[ro.build.version.release]: [15]
[ro.build.display.id]: [FP5.VT2E.C.059.20250908]

Device Model

[ro.product.brand]: [Fairphone]
[ro.build.product]: [FP5]

How To Reproduce

Invoke the chooser:

Expected Behaviour

I should be able to see how many accounts are registered, and be able to choose another without first invoking an overlay. Otherwise, significant time is lost choosing accounts.

To demonstrate that this opinion is not merely my own, see versionCode=42544822 of com.microsoft.office.outlook:

Actual Behaviour

The update removes the sidebar, and introduces an overlay:

This overlay actually provides more information, which has significant use:

However, for those who switch between e-mail accounts often, and those without tens of e-mail accounts, the sidebar is an improvement over the overlay.

Start by reproducing the account chooser on Thunderbird Android 12.0b4 using the reported Fairphone 5 and Android 15 details, then inspect the account-switching UI entry point. Compare the current overlay with the reported sidebar workflow and use the issue screenshots and expected behavior to define completion; no source file or test is identified in the report.