There may well be multiple code paths that can end up hitting this exception from deep inside dwrite; but at least one of them appears to be gfxDWriteFontList::CreateFontEntry, which may make several DWrite API calls that might try to access font data. Any such call seems to be at risk of triggering an exception in case of disk errors or similar failures, so let's try wrapping them with an exception handler.
Bug 1529794 Comment 3 Edit History
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There may well be multiple code paths that can end up hitting this exception from deep inside dwrite; but at least one of them appears to be through gfxDWriteFontList::CreateFontEntry, which may make several DWrite API calls that might try to access font data. Any such call seems to be at risk of triggering an exception in case of disk errors or similar failures, so let's try wrapping them with an exception handler.