This bug is for crash report bp-0a2eeb7f-174b-4fcb-b6bd-059f20190403.

Top 10 frames of crashing thread:

0 XUL mozilla::dom:: dom/localstorage/ActorsParent.cpp:6696
1 XUL mozilla::dom:: dom/localstorage/ActorsParent.cpp:5783
2 XUL non-virtual thunk to mozilla::dom:: dom/localstorage/ActorsParent.cpp:5767
3 XUL mozilla::dom::PBackgroundLSRequestParent::OnMessageReceived ipc/ipdl/PBackgroundLSRequestParent.cpp:134
4 XUL mozilla::ipc::MessageChannel::DispatchMessage ipc/glue/MessageChannel.cpp:2151
5 XUL mozilla::ipc::MessageChannel::MessageTask::Run ipc/glue/MessageChannel.cpp:1937
6 XUL nsThread::ProcessNextEvent xpcom/threads/nsThread.cpp:1180
7 XUL NS_ProcessNextEvent xpcom/threads/nsThreadUtils.cpp:482
8 XUL mozilla::ipc::MessagePumpForNonMainThreads::Run ipc/glue/MessagePump.cpp:333
9 XUL nsThread::ThreadFunc ipc/chromium/src/base/message_loop.cc:315

This is a perma-insta-startup crash I get on my main nightly profile. Other reports from me:

bp-9096f10a-f351-440f-88fc-4e8dc0190403
bp-5f234c1f-186f-4033-8e92-b6e9a0190403
bp-5e7f29e1-b0b7-4db3-945c-9398f0190403
bp-74491325-738a-47dc-a610-2b81f0190403
bp-8e714bc4-e9c2-4706-a97a-0e5fd0190403
bp-9ba575e4-02e2-40d5-ac4c-4e1c50190403
bp-7bf363c8-6a15-473c-9ebd-39d890190403

Nightly does start fine in safe mode however.

This looks like the same bug I just filed as bug 1541681.

Nightly crashed while restoring my session (just like in Bug 1541681). I could start it in safe mode, and cleared my session. Restarted in normal mode and it was fine. I tried loading each of my pinned tabs by hand and it crashed when I tried to load mozilla.slack.com. I can reliably reproduce the crash when Slack loads.

Hey, sorry for the trouble. We are disabling the assertion in optimized builds in bug 1541681.
You can disable new local storage implementation by setting dom.storage.next_gen to false until the assertion is disabled in next Nightly.