Mozilla is adding a plugin hang UI to Firefox for Windows. When a plugin such as Adobe Flash stops responding, Firefox will show a dialog that names the plugin and lets you stop it right away, instead of leaving the whole browser frozen while it waits.
The problem it solves
Many people still need plugins for everyday tasks such as watching videos. When a plugin hangs, Firefox appears locked too. Right now the browser waits 45 seconds before it kills the unresponsive plugin, and during that time it isn’t obvious that the plugin, not Firefox, is at fault. Mozilla’s goal with the new feature is to make that clear and to let you end the plugin immediately if you don’t want to wait.
How the plugin hang UI works
- When a plugin stops responding for a short time, a dialog appears over the browser.
- It tells you which plugin is not responding.
- You can stop the plugin right away, or continue and wait to see if it recovers.
- If you do nothing, Firefox still kills the plugin automatically after a longer timeout.
Stopping the plugin doesn’t take Firefox down with it, because plugins run in their own process. And because Firefox’s main thread is the thing that’s stuck, the dialog can’t be drawn by Firefox itself. Mozilla solved this with a small separate Windows program, plugin-hang-ui.exe, that talks to Firefox and shows the dialog.
Settings you can change in about:config
The feature is on by default, and a few preferences control it:
- Type
about:configin the address bar and accept the warning. - Search for
dom.ipc.plugins. One preference sets how many seconds Firefox waits after detecting a hang before it shows the dialog; a value of 0 turns the dialog off. dom.ipc.plugins.timeoutSecs: the seconds before a hung plugin is killed automatically. With the new UI, the countdown starts once the dialog is shown.dom.ipc.plugins.hangUIMinDisplaySecs: the minimum time the dialog stays on screen.
Mozilla’s test plan also notes you can disable the feature by setting dom.ipc.plugins.timeoutSecs lower than dom.ipc.plugins.hangUIMinDisplaySecs. New to these settings? Read our guide on how to use Firefox’s about:config first.
Availability
The plugin hang UI is for Firefox on Windows only, and it covers Flash hangs. Mozilla’s feature page lists Firefox 19 as the release target, and the feature is available from the Firefox 19 beta onward.
Today
Plugins such as Flash are no longer supported in today’s Firefox, so this dialog has nothing left to manage. If Firefox feels sluggish on a modern PC, Windows power features can be the cause; see our tips to stop Windows 11 throttling Firefox.
