Sometimes my Iceweasel (unbranded firefox) web browser seems sluggish after rendering flash heavy web page or stops responding all together. I hope this behavior is not uncommon at all.
Instead of waiting for(ever) the browser to start responding normally I resort killing the web browser with killall 11 (eleven) HUP signal. After-all its me who is uses the computer not the other way around. ;o)
killall -11 firefox-bin
Note: Please note that -11 is hyphen followed by two numeric one's not ' l ' English alphabet.