Sandboxie 5.31.6 x64 on Windows 10 1909, FF 70.0.1 x64, similar issues I have reported previously in windows 7 and windows 10 1809. Firefox safemode does not fix this... resetting firefox does not fix this, deleting sandbox and starting with a default profile does not fix this. It always happens after loading a number of tabs at once, say 4-12 tabs of www.whatreallyhappened.com... that recreated it for me. Other times it just starts randomly. Setting Firefox Sandbox to 0 does not fix this. Running firefox outside of sandboxie fixes this.