Firefox 3 Beta 4 'page redirecting' silliness

Since installing Firefox 3 Beta 4, I've seen the following IE-inspired pop-up far too often:

I see this when performing the following all-too-common actions:

• Click a link from within Gmail
  
• Open a new tab and manually enter a URL and then tap Enter
  

Enough already. This thing pops up too often and of course Firefox won't load the offending site until I've clicked Allow. There's no "Always Allow" or any obvious UI for turning this feature off.

Any ideas?

Update: A few people have already emailed me with the location in FF3 Options where this is turned off:

Thanks for that. But I'm still curious: Why was this never an issue in FF2 (or, I believe, previous FF3 betas)? I'm curious what's changed.