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Linux Desktop

When Flatpak Firefox crashes on its very first launch — it turned out the RTX 40 was running on nouveau

Environment: Kubuntu 26.04 LTS · KDE Plasma 6 · NVIDIA RTX 4070 Ti SUPER · Flatpak

TL;DR

If Flatpak Firefox crashes on its very first launch, before you blame flatpak, check which driver the GPU is bound to.

lspci -k | grep -A3 "VGA"

If it's an RTX 40 card reading Kernel driver in use: nouveau, the proprietary driver isn't installed and GPU-accelerated rendering is dying. With Secure Boot off you can just install it:

mokutil --sb-state          # expect: SecureBoot disabled
sudo ubuntu-drivers autoinstall

Reboot and Firefox launches normally.

The symptom

This was right after ripping out snap and reinstalling firefox, telegram, and obsidian as Flatpaks. The user launched Firefox and it crashed immediately on first run, popping the Firefox Crash Reporter. Every relaunch died the same way.

The misdiagnosis: "it must be the flatpak packaging"

Since we'd just switched to flatpak, I suspected the flatpak sandbox or packaging first. That was wrong.

Firefox — flatpak, deb, or snap — will crash in some form whenever the GPU-accelerated rendering path dies. The recent switch to flatpak was just the salient thing to blame; the actual cause sat at a much lower layer that has nothing to do with how the app is packaged.

Root cause: nouveau has essentially no 3D acceleration on RTX 40

I asked the user to check which kernel driver the GPU was bound to.

lspci -k | grep -A3 "VGA"

The RTX 4070 Ti SUPER was bound to nouveau (the open-source default), not nvidia. There wasn't even an nvidia-smi — meaning the proprietary driver wasn't installed at all.

nouveau barely supports 3D acceleration on recent NVIDIA GPUs, especially the Ada Lovelace RTX 40 series. Firefox's GPU-accelerated rendering path (WebRender and friends) simply died in that state. This wasn't a flatpak problem — any app needing hardware acceleration would have blown up (Electron-based Obsidian uses the same renderer family and was potentially at the same risk).

The fix

First, check the Secure Boot state.

mokutil --sb-state
# SecureBoot disabled

With Secure Boot off, unsigned kernel modules load directly, so you can install the driver without the MOK (Machine Owner Key) enrollment dance. I asked the user to autoinstall.

sudo ubuntu-drivers autoinstall

For this hardware the command picked nvidia-driver-595-open as the recommended driver. After a reboot the user confirmed Firefox launched fine.

This episode bumped "install the NVIDIA driver" from a someday task to the top-priority item blocking any GPU-accelerated app, and it got handled on the spot.

Verifying

The current state the user sent back:

$ lspci -k | grep -A3 VGA
01:00.0 VGA compatible controller: NVIDIA Corporation AD103 [GeForce RTX 4070 Ti SUPER]
	Kernel driver in use: nvidia
	Kernel modules: nvidiafb, nouveau, nvidia_drm, nvidia

Kernel driver in use: nvidia — the nouveau module still exists on the system (it's listed among the kernel modules), but the one actually bound and in use is nvidia. It's held without regressing.

Takeaways / checklist

  • If a Flatpak app crashes the instant it launches, check which graphics driver is bound with lspci -k before blaming flatpak. Firing up a GPU-accelerated app right after a fresh install, with no proprietary driver, blows up exactly like this.
  • The newer the NVIDIA GPU (RTX 40 and up), the more painful nouveau's 3D-acceleration gap — put the NVIDIA driver install at the top of the list right after a fresh install.
  • With Secure Boot off, ubuntu-drivers autoinstall finishes with no MOK enrollment.