According to this startup profile, SearchService.jsm runs during startup and imports osfile.jsm. We should migrate this to the new IOUtils replacement for osfile.jsm when possible.

Stack:

XREMain::XRE_main []
XREMain::XRE_main(int, char**, mozilla::BootstrapConfig const&) [libxul.so]
XREMain::XRE_mainRun() [libxul.so]
nsAppStartup::Run() [libxul.so]
nsBaseAppShell::Run() [libxul.so]
MessageLoop::Run() [libxul.so]
mozilla::ipc::MessagePump::Run(base::MessagePump::Delegate*) [libxul.so]
nsThread::ProcessNextEvent(bool, bool*) [libxul.so]
mozilla::ipc::MessageChannel::MessageTask::Run() [libxul.so]
mozilla::ipc::MessageChannel::DispatchMessage(IPC::Message&&) [libxul.so]
mozilla::layers::PCompositorManagerChild::OnMessageReceived(IPC::Message const&) [libxul.so]
PCompositorBridge::Msg_DidComposite []
mozilla::layers::PCompositorBridgeChild::OnMessageReceived(IPC::Message const&) [libxul.so]
mozilla::layers::CompositorBridgeChild::RecvDidComposite(mozilla::layers::LayersId const&, mozilla::layers::BaseTransactionId<mozilla::layers::TransactionIdType> const&, mozilla::TimeStamp const&, mozilla::TimeStamp const&) [libxul.so]
mozilla::layers::ClientLayerManager::DidComposite(mozilla::layers::BaseTransactionId<mozilla::layers::TransactionIdType>, mozilla::TimeStamp const&, mozilla::TimeStamp const&) [libxul.so]
nsView::DidCompositeWindow(mozilla::layers::BaseTransactionId<mozilla::layers::TransactionIdType>, mozilla::TimeStamp const&, mozilla::TimeStamp const&) [libxul.so]
nsContentUtils::RemoveScriptBlocker() [libxul.so]
DelayedFireDOMPaintEvent::Run() [libxul.so]
nsPresContext::FireDOMPaintEvent(nsTArray<nsRect>*, mozilla::layers::BaseTransactionId<mozilla::layers::TransactionIdType>, mozilla::TimeStamp) [libxul.so]
mozilla::EventDispatcher::DispatchDOMEvent(nsISupports*, mozilla::WidgetEvent*, mozilla::dom::Event*, nsPresContext*, nsEventStatus*) [libxul.so]
EventDispatcher::Dispatch []
EventDispatcher::Dispatch MozAfterPaint []
mozilla::EventDispatcher::Dispatch(nsISupports*, nsPresContext*, mozilla::WidgetEvent*, mozilla::dom::Event*, nsEventStatus*, mozilla::EventDispatchingCallback*, nsTArray<mozilla::dom::EventTarget*>*) [libxul.so]
mozilla::EventTargetChainItem::HandleEventTargetChain(nsTArray<mozilla::EventTargetChainItem>&, mozilla::EventChainPostVisitor&, mozilla::EventDispatchingCallback*, mozilla::ELMCreationDetector&) [libxul.so]
EventListener.handleEvent []
mozilla::EventListenerManager::HandleEventInternal(nsPresContext*, mozilla::WidgetEvent*, mozilla::dom::Event**, mozilla::dom::EventTarget*, nsEventStatus*, bool) [libxul.so]
mozilla::dom::EventListener::HandleEvent(mozilla::dom::BindingCallContext&, JS::Handle<JS::Value>, mozilla::dom::Event&, mozilla::ErrorResult&) [libxul.so]
JS::Call(JSContext*, JS::Handle<JS::Value>, JS::Handle<JS::Value>, JS::HandleValueArray const&, JS::MutableHandle<JS::Value>) [libxul.so]
js::RunScript []
js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) [libxul.so]
bound [self-hosted:839:25]
0xff4eaa5dbc7 []
js::jit::DoCallFallback(JSContext*, js::jit::BaselineFrame*, js::jit::ICCall_Fallback*, unsigned int, JS::Value*, JS::MutableHandle<JS::Value>) [libxul.so]
js::RunScript []
_delayedStartup [chrome://browser/content/browser.js:1923:17]
delayedStartupInit [chrome://browser/content/browser.js:3918:20]
_updateURLBarPlaceholderFromDefaultEngine [chrome://browser/content/browser.js:4049:49]
js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) [libxul.so]
Interpret(JSContext*, js::RunState&) [libxul.so]
js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) [libxul.so]
XPC_WN_CallMethod(JSContext*, unsigned int, JS::Value*) [libxul.so]
XPCWrappedNative::CallMethod(XPCCallContext&, XPCWrappedNative::CallMode) [libxul.so]
NS_InvokeByIndex [libxul.so]
SharedStub [libxul.so]
PrepareAndDispatch [libxul.so]
XPCWrappedJS method call []
nsXPCWrappedJS::CallMethod(unsigned short, nsXPTMethodInfo const*, nsXPTCMiniVariant*) [libxul.so]
JS_CallFunctionValue(JSContext*, JS::Handle<JSObject*>, JS::Handle<JS::Value>, JS::HandleValueArray const&, JS::MutableHandle<JS::Value>) [libxul.so]
js::RunScript []
getDefault [resource://gre/modules/SearchService.jsm:3103:18]
init [resource://gre/modules/SearchService.jsm:2271:12]
_init [resource://gre/modules/SearchService.jsm:536:13]
> _readCacheFile [resource://gre/modules/SearchService.jsm:1557:22]
js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) [libxul.so]
Interpret(JSContext*, js::RunState&) [libxul.so]
js::NativeGetExistingProperty(JSContext*, JS::Handle<JSObject*>, JS::Handle<js::NativeObject*>, JS::Handle<js::Shape*>, JS::MutableHandle<JS::Value>) [libxul.so]
js::CallGetter(JSContext*, JS::Handle<JS::Value>, JS::Handle<JS::Value>, JS::MutableHandle<JS::Value>) [libxul.so]
js::InternalCallOrConstruct(JSContext*, JS::CallArgs const&, js::MaybeConstruct, js::CallReason) [libxul.so]
mozilla::dom::module_getter::ModuleGetter(JSContext*, unsigned int, JS::Value*) [libxul.so]
mozJSComponentLoader::Import(JSContext*, nsTSubstring<char> const&, JS::MutableHandle<JSObject*>, JS::MutableHandle<JSObject*>, bool) [libxul.so]
profiler_get_backtrace() [libxul.so]
Registers::SyncPopulate() [libxul.so]

We need to remove the OS.File import in SearchService.jsm: https://searchfox.org/mozilla-central/rev/9c72508fcf2bba709a5b5b9eae9da35e0c707baa/toolkit/components/search/SearchService.jsm#19

We also need to update the usage of OS.File here: https://searchfox.org/mozilla-central/rev/9c72508fcf2bba709a5b5b9eae9da35e0c707baa/toolkit/components/search/SearchService.jsm#2610

This can be updated to instead use AsyncShutdown.profileBeforeChange.addBlocker instead, and we will need to import that module.

(In reply to Emma Malysz from comment #1)

[snip]
This can be updated to instead use AsyncShutdown.profileBeforeChange.addBlocker instead, and we will need to import that module.

The shutdown blocking code also needs to be updated to allow IO to run during this phase (currently blocking bug 1649595 from landing).

Ah, got it. I thought that had been covered by Bug 1659838. I can follow a file up bug

After speaking with :masterwayz, we are going to handle both of these removals in Bug 1671274 because they rely on each other