gBrowser

Tabbrowser.sys.mjs defines the Tabbrowser class, shared across windows: as a system module it loads once per process, so there is one Tabbrowser class for the whole browser. The Tabbrowser manages tabs and provides an interface to operate on tabs. It also manages the underlying infrastructure for switching tabs, adding tabs, removing tabs, knowing about tab switches, etc. Each window creates its own Tabbrowser instance during startup and exposes that instance in the window scope as gBrowser.

What does the name gBrowser stand for?

What does the g in gBrowser stand for? It’s an old Mozilla convention and g stands for global. It’s a way of indicating inside of the variable name that something is globally scoped. In this case it is global to the browser window and every single tab of the window will be managed through that window’s gBrowser.

What does the browser in gBrowser stand for? browser is an element that knows how to render web content. At some point in its lineage, Firefox didn’t have tabs. There was one browser per window, and that individual browser was called gBrowser. Today’s gBrowser forwards a number of calls to the current selectedBrowser, which is an actual <xul:browser> element.

Relationship between browser and gBrowser

<xul:browser> is a XUL element that can load web pages, make HTTP requests and respond accordingly. It is conceptually similar to an iframe except that it contains additional methods and has elevated privileges. In Firefox, each tab is associated with one <xul:browser>, and gBrowser owns all of the browsers.