"Firefox prevented this site (chrispederick.com) from asking you to install software on your computer."
So, apparently sites that aren't in a whitelist aren't even allowed to ask if I want to install something. I apparently have to tinker with the options to add the site, which at first glance would let it auto-install updates but merely lets it get as far as prompting me.
Which leads to the next annoyance: a "Software Installation" prompt that forces me to wait 5 seconds before I can click "Install" every time that window gets focus. So alt-tabbing between it and Semagic resets the 5-second counter.
Oh, and then it wants a restart, and doesn't think to show a "Restart Later" button. Now, closing that pop-up by other means doesn't restart the browser, but seriously folks, *think* about the user interface.