lock

1. Right-click on Lock button -> select 'Restart Screensaver Daemon'
2. Check if the xscreensaver daemon is running. At a terminal window, type: pgrep -u your_username xscreensaver -l

where your_username is substituted with your username.

...

With Netscape:

rm $HOME/.netscape/lock or rm ~/.netscape/lock

For Mozilla:

rm $HOME/.mozilla/*/*/lock or rm ~/.mozilla/*/*/lock

For Firefox:

rm $HOME/.mozilla/firefox/*/lock rm $HOME/.mozilla/firefox/*/...