Methods are provided for thread-agile script execution. Thread-agile script execution may be carried out by receiving, in a message queue, a message for an instance of a script and determining whether the web browser has a stored state object for the instance of the script identified by the message. If the web browser has a stored state object for the script, thread-agile script execution may be carried out by retrieving the state object; preparing a thread available from a thread pool for execution of the instance of the script in dependence upon the state object and an execution context for the instance of the script; providing, to an execution engine for executing the script, the state object and the prepared thread; and passing the message to the execution engine.