Firefox crashes when switching VMs

[llewelld]

✅ Checklist

• I have searched open and closed issues for duplicates.
• This is a problem observed when using a Data Safe Haven.
• I can reproduce this with the latest version.
• I have read through the documentation.
• This isn't an open-ended question (open a discussion if it is).

💻 System information

• Operating System: Ubuntu 24.04.4 LTS
• Data Safe Haven version: 5.7.1
• Browser details: Firefox 152.0.4 (64-bit)

🚫 Describe the problem

After deploying a new VM with a new configuration, switching from the old VM in Guacamole to the new VM resulted in a desktop with broken browser.

Steps to reproduce:

1. Deploy an SRE with a single Standard_D8ds_v5 VM.
2. Log in to the desktop of the Standard_D8ds_v5 VM using Guacamole.
3. Use the browser for a bit (e.g. to access Gitea).
4. Log out of the desktop.
5. Redeploy the SRE with an additional Standard_F32s_v2 VM.
6. Log in to the desktop of the Standard_F32s_v2 VM using Guacamole.
7. Attempt to open and use the browser (e.g. to access Gitea).

Expected outcome:

The browser works well and without any issues.

Actual outcome:

The browser takes an extended period of time to load. Browser usage is unstable with rendering failures and crashes that take out the entire browser.

The browser also fails to quit properly, which can prevent the browser being restarted.

Restarting from the command line shows permission and directory access errors, as shown in the screenshot.

🚂 Workarounds or solutions

The issue seems to be due to the snap package storing profile information that's specific to the platform in use. Wiping the snap configuration and restarting Firefox seems to address the issue:

$ killall firefox
$ mv ~/snap/firefox ~/snap_firefox_backup_01

[jemrobinson]

This happens because the Firefox profile lives in your home directory which is shared across VMs. It is writing lock files or similar that say "I'm already running" but there's no corresponding process on the new VM. If you close Firefox on the old VM before doing this, the problem should disappear.