Happens on Linux, with latest Nightly, fr and en-US locales.
Andreea, is this a regression in Firefox on Linux? Or is it caused by the private browsing tests which run first on Linux?
I will put this as a task for next week.
Henrik, the preferences tests are ran way before the private browsing ones. In between there are also Toolbar, TabbedBrowsing, TechnicalTools, Search, Popups, Layout, TabbedView and then the PB ones.
The sprint entry is covered by the meta bug.
Didn't happen again. Closing as WFM for now.