I’ve had this problem lately with Firefox. When I play a YouTube video and close the tab before the end of the video I still hear sound for several seconds. This has been really annoying and I haven’t been able to figure it out until recently.

It appears that there is a bug that was introduced in one of the 3.0.* Firefox releases and only happens when Firefox is used in tandem with the Flashblock extension.

A little back story first. Autoplaying sound/video on websites annoys the hell out of me anyway so I install Flashblock in every Firefox install I have. If you install this plugin it prevents all Flash istances on a page from loading. You simply have to click once to activate the video. Not only does this prevent Flash content from autoloading, it also seems to reduce the memory footprint as well.

Back to the fix for the problem. You can read all the gory details on Bugzilla.

Fix Option 1

-Disable Flashblock

This option is unacceptable. Must have Flashblock

Fix Option 2

-Wait for Firefox 3.0.7. Should be released on March 7th.

update: The Firefox 3.0.7 update did indeed fix this very annoying problem.