2030462 - Couldn't load XPCOM after first Firefox download

Status: NEW

(Firefox :: Installer, defect, P3)

Description

[Helena Ballent [:hballent]]

Attachment: 79736230558__E98B63EE-F0E2-40B9-A970-C9C76C489087.jpeg

DESCRIPTION

After running the Firefox installer on Windows, the browser fails to launch. A modal dialog titled "Firefox" appears with the message "Couldn't load XPCOM." and an OK button. Clicking OK dismisses the dialog and the browser does not open. The same error occurs when launching from the Start Menu shortcut post-install.

ACTUAL RESULT
Dialog appears: "Couldn't load XPCOM." Firefox does not open. Error persists on every subsequent launch attempt.

EXPECTED RESULT
Firefox browser window opens successfully after installation completes.

Claude's Theory:
"The installer file used (Firefox Installer.exe, 488 KB) is a stub installer — a small bootstrapper that downloads the full Firefox package (~65 MB) from Mozilla's servers at runtime. It is assumed that this secondary network download failed silently during installation.

This assumption is supported by the fact that the "Couldn't load XPCOM." error appeared at the end of the installer run — before Firefox was ever launched — suggesting the XPCOM runtime and other core components were never written to disk.

If confirmed, the defect is not the missing files themselves, but the installer's failure to surface a meaningful error when the download is interrupted — instead proceeding to create Start Menu shortcuts and exit without warning, giving the user the false impression that installation succeeded."

The user redownloaded Firefox and the issue was resolved.

Comment 1

[Helena Ballent [:hballent]]

Firefox version 149.0.2

Device Name SWIHQLT14
Full device name  SWIHQLT14.swi.net
Processor   11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz 2.80 GHz
Installed RAM     16.0 GB (15.7 GB usable)
Storage     477 GB SSD NVMe PC SN530 NVMe WDC 512GB
Graphics Card     Intel(R) Iris(R) Xe Graphics (128 MB)
Device ID   6CFA43A6-4D51-403F-B0A5-437F4369503A
Product ID  00355-62733-71393-AAOEM
System Type 64-bit operating system, x64-based processor
Pen and touch     Touch support with 10 touch points

Edition     Windows 10 Pro
Version     22H2
Installed on      ‎1/‎8/‎2022
OS Build    19045.6456

Comment 2

[Nika Layzell [:nika] (ni? for response)]

An error like "Couldn't load XPCOM" is actually a installer issue, as it means that we failed to load the XUL.dll file from disk early during startup. The dialog is shown here: https://searchfox.org/firefox-main/rev/662d18616bbb2da4c5a8758da50fc9d591d18c19/browser/app/nsBrowserApp.cpp#287

There's nothing we can really do to recover if the install is borked in this way, as we haven't even loaded 99% of the Gecko code yet. Maybe the installer could be doing better install verification or similar?

Comment 3

[Harshit Sohaney [:hsohaney]]

This is an error that the DI team is aware of and is actively tracking. We'll be working on a fix soon!