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+# Timeline Markers
+
+## Common
+
+* DOMHighResTimeStamp start
+* DOMHighResTimeStamp end
+* DOMString name
+* object? stack
+* object? endStack
+* unsigned short processType;
+* boolean isOffMainThread;
+
+The `processType` a GeckoProcessType enum listed in xpcom/build/nsXULAppAPI.h,
+specifying if this marker originates in a content, chrome, plugin etc. process.
+Additionally, markers may be created from any thread on those processes, and
+`isOffMainThread` highights whether or not they're from the main thread. The most
+common type of marker is probably going to be from a GeckoProcessType_Content's
+main thread when debugging content.
+
+## DOMEvent
+
+Triggered when a DOM event occurs, like a click or a keypress.
+
+* unsigned short eventPhase - a number indicating what phase this event is
+  in (target, bubbling, capturing, maps to Ci.nsIDOMEvent constants)
+* DOMString type - the type of event, like "keypress" or "click"
+
+## Reflow
+
+Reflow markers (labeled as "Layout") indicate when a change has occurred to
+a DOM element's positioning that requires the frame tree (rendering
+representation of the DOM) to figure out the new position of a handful of
+elements. Fired via `PresShell::DoReflow`
+
+## Paint
+
+* sequence<{ long height, long width, long x, long y }> rectangles - An array
+  of rectangle objects indicating where painting has occurred.
+
+## Styles
+
+Style markers (labeled as "Recalculating Styles") are triggered when Gecko
+needs to figure out the computational style of an element. Fired via
+`RestyleTracker::DoProcessRestyles` when there are elements to restyle.
+
+* DOMString restyleHint - A string indicating what kind of restyling will need
+  to be processed; for example "eRestyle_StyleAttribute" is relatively cheap,
+  whereas "eRestyle_Subtree" is more expensive. The hint can be a string of
+  any amount of the following, separated via " | ". All future restyleHints
+  are from `RestyleManager::RestyleHintToString`.
+
+  * "eRestyle_Self"
+  * "eRestyle_Subtree"
+  * "eRestyle_LaterSiblings"
+  * "eRestyle_CSSTransitions"
+  * "eRestyle_CSSAnimations"
+  * "eRestyle_SVGAttrAnimations"
+  * "eRestyle_StyleAttribute"
+  * "eRestyle_StyleAttribute_Animations"
+  * "eRestyle_Force"
+  * "eRestyle_ForceDescendants"
+
+
+## Javascript
+
+`Javascript` markers are emitted indicating when JS execution begins and ends,
+with a reason that triggered it (causeName), like a requestAnimationFrame or
+a setTimeout.
+
+* string causeName - The reason that JS was entered. There are many possible
+  reasons, and the interesting ones to show web developers (triggered by content) are:
+
+  * "\<script\> element"
+  * "EventListener.handleEvent"
+  * "setInterval handler"
+  * "setTimeout handler"
+  * "FrameRequestCallback"
+  * "EventHandlerNonNull"
+  * "promise callback"
+  * "promise initializer"
+  * "Worker runnable"
+
+  There are also many more potential JS causes, some which are just internally
+  used and won't emit a marker, but the below ones are only of interest to
+  Gecko hackers, most likely
+
+  * "promise thenable"
+  * "worker runnable"
+  * "nsHTTPIndex set HTTPIndex property"
+  * "XPCWrappedJS method call"
+  * "nsHTTPIndex OnFTPControlLog"
+  * "XPCWrappedJS QueryInterface"
+  * "xpcshell argument processing”
+  * "XPConnect sandbox evaluation "
+  * "component loader report global"
+  * "component loader load module"
+  * "Cross-Process Object Wrapper call/construct"
+  * "Cross-Process Object Wrapper ’set'"
+  * "Cross-Process Object Wrapper 'get'"
+  * "nsXULTemplateBuilder creation"
+  * "TestShellCommand"
+  * "precompiled XUL \<script\> element"
+  * "XBL \<field\> initialization "
+  * "NPAPI NPN_evaluate"
+  * "NPAPI get"
+  * "NPAPI set"
+  * "NPAPI doInvoke"
+  * "javascript: URI"
+  * "geolocation.always_precise indexing"
+  * "geolocation.app_settings enumeration"
+  * "WebIDL dictionary creation"
+  * "XBL \<constructor\>/\<destructor\> invocation"
+  * "message manager script load"
+  * "message handler script load"
+  * "nsGlobalWindow report new global"
+
+## GarbageCollection
+
+Emitted after a full GC cycle has completed (which is after any number of
+incremental slices).
+
+* DOMString causeName - The reason for a GC event to occur. A full list of
+  GC reasons can be found [on MDN](https://developer.mozilla.org/en-US/docs/Tools/Debugger-API/Debugger.Memory#Debugger.Memory_Handler_Functions).
+* DOMString nonincremenetalReason - If the GC could not do an incremental
+  GC (smaller, quick GC events), and we have to walk the entire heap and
+  GC everything marked, then the reason listed here is why.
+
+## nsCycleCollector::Collect
+
+An `nsCycleCollector::Collect` marker is emitted for each incremental cycle
+collection slice and each non-incremental cycle collection.
+
+# nsCycleCollector::ForgetSkippable
+
+`nsCycleCollector::ForgetSkippable` is presented as "Cycle Collection", but in
+reality it is preparation/pre-optimization for cycle collection, and not the
+actual tracing of edges and collecting of cycles.
+
+## ConsoleTime
+
+A marker generated via `console.time()` and `console.timeEnd()`.
+
+* DOMString causeName - the label passed into `console.time(label)` and
+  `console.timeEnd(label)` if passed in.
+
+## TimeStamp
+
+A marker generated via `console.timeStamp(label)`.
+
+* DOMString causeName - the label passed into `console.timeStamp(label)`
+  if passed in.
+
+## document::DOMContentLoaded
+
+A marker generated when the DOMContentLoaded event is fired.
+
+## document::Load
+
+A marker generated when the document's "load" event is fired.
+
+## Parse HTML
+
+## Parse XML
+
+## Worker
+
+Emitted whenever there's an operation dealing with Workers (any kind of worker,
+Web Workers, Service Workers etc.). Currently there are 4 types of operations
+being tracked: serializing/deserializing data on the main thread, and also
+serializing/deserializing data off the main thread.
+
+* ProfileTimelineWorkerOperationType operationType - the type of operation
+  being done by the Worker or the main thread when dealing with workers.
+  Can be one of the following enums defined in ProfileTimelineMarker.webidl
+  * "serializeDataOffMainThread"
+  * "serializeDataOnMainThread"
+  * "deserializeDataOffMainThread"
+  * "deserializeDataOnMainThread"
+
+## Composite
+
+Composite markers trace the actual time an inner composite operation
+took on the compositor thread. Currently, these markers are only especially
+interesting for Gecko platform developers, and thus disabled by default.
+
+## CompositeForwardTransaction
+
+Markers generated when the IPC request was made to the compositor from
+the child process's main thread.