Steps to reproduce: 1) open two windows 2) in the first window, browse to a page and hit ctrl-s 3) leave the modal file chooser open and switch to the second window 4) browse around to sites with plugins like youtube & yahoo, use multiple tabs, close tabs, etc. 5) try switching back and forth between the two windows occasionally. Various problems crop up. Video on youtube continue to play even after the tab is closed is the most obvious. Sometimes you'll get a crash without a crash report as well. Related: Bug 470487
Old bug, cannot reproduce on nightly 21.0a1 (2013-01-27) Win 7.
Resolving old bugs which are likely not relevant any more, since NPAPI plugins are deprecated.