TL;DR: Beware! Tried to send 32 tabs from Windows VM browser instance to Fedora browser instance. Entire VM crashed then browser process on Linux host crashed.

Before winter break I virtualized a Windows PC and set it up as a KVM/QEMU guest on Fedora running on the same hardware. Got IOMMU/Vfio passthrough working on guest. Loving the near-native performance. Seems really solid. Left it running continuously for several days, compiled multiple projects. Got over a week of usage with VM and had no issues.

Set up a new Firefox account for work to accommodate new workflow. Set it up to only sync certain items, but I forget which. Can't tell from account management page. Logged in on browser instances on both host and guest. I'd accumulated some tabs on guest instance that I wanted to bookmark on host instance. Tried a single tab using Send Tab to Device. Worked fine. Selected all tabs, did Send 32 Tabs to Device. Tabs appeared on host instance, appeared to be loading. Then my external monitor went black. VM had crashed. Browser instance on host stopped responding moments later, then closed itself after a brief time.

Both host and guest running 133.0.3. Host instance was installed from flatpak.

Nothing notable in Windows System log except for the usual "previous system shutdown was unexpected" EventLog and Kernel-Power events.

Edit: Was able to reproduce the VM crash with only 10 tabs. At 20 tabs, the VM crashed and the host browser process died as in the original incident.