BrowsingContext and WindowContext

The BrowsingContext is the Gecko representation of the spec-defined Browsing Context object.

The Browsing Context Tree

BrowsingContext and WindowContext objects form a tree, corresponding to the tree of frame elements which was used to construct them.


Loading the HTML documents listed here, would end up creating a set of BrowsingContexts and WindowContexts forming the tree.

<!-- -->
<iframe src="frame1.html"></iframe>
<iframe src=""></iframe>

<!-- -->
<iframe src=""></iframe>

<!-- -->
digraph browsingcontext {
node [shape=rectangle]

"BC1" [label="BrowsingContext A"]
"BC2" [label="BrowsingContext B"]
"BC3" [label="BrowsingContext C"]
"BC4" [label="BrowsingContext D"]
"BC5" [label="BrowsingContext E"]
"BC6" [label="BrowsingContext F"]

"WC1" [label="WindowContext\n("]
"WC2" [label="WindowContext\n("]
"WC3" [label="WindowContext\n("]
"WC4" [label="WindowContext\n("]
"WC5" [label="WindowContext\n(about:blank)"]
"WC6" [label="WindowContext\n(about:blank)"]

"BC1" -> "WC1";
"WC1" -> "BC2";
"WC1" -> "BC3";
"BC2" -> "WC2";
"BC3" -> "WC3";
"WC2" -> "BC4";
"BC4" -> "WC4";
"WC3" -> "BC5";
"BC5" -> "WC5";
"WC3" -> "BC6";
"BC6" -> "WC6";

Synced Fields

WIP - In-progress documentation at

API Documentation

class BrowsingContext

This is a synced-context type. Instances of it will exist in every “relevant” content process for the navigation.

Instances of BrowsingContext created in the parent processes will be CanonicalBrowsingContext.

WindowContext *GetParentWindowContext()

Get the parent WindowContext embedding this context, or nullptr, if this is the toplevel context.

WindowContext *GetTopWindowContext()

Get the toplevel WindowContext embedding this context, or nullptr if this is the toplevel context.

This is equivalent to repeatedly calling GetParentWindowContext() until it returns nullptr.

BrowsingContext *GetParent()
BrowsingContext *Top()
static already_AddRefed<BrowsingContext> Get(uint64_t aId)

Look up a specific BrowsingContext by it’s unique ID. Callers should check if the returned context has already been discarded using IsDiscarded before using it.

class CanonicalBrowsingContext : public BrowsingContext

When a BrowsingContext is constructed in the parent process, it is actually an instance of CanonicalBrowsingContext.

Due to being in the parent process, more information about the context is available from a CanonicalBrowsingContext.

class WindowContext
class WindowGlobalParent : public WindowContext, public WindowGlobalActor, public PWindowGlobalParent
class WindowGlobalChild : public WindowGlobalActor, public PWindowGlobalChild