I see both sides of this topic, and don't really feel strongly either way.

Here's a blog post from a Mozilla person explaining the reasoning a bit. I've been following this discussion elsewhere, and here's a response to the blog post from Hacker News:

I have to say that this article is actually quite terrible, as is the opinion that any option that might ever be confusing to a user is an option that shouldn't ship with the product. The thesis of the article is:

"Well, we have met the enemy, and he is us.* In the currently shipping version, Firefox ships with many options that will render the browser unusable to most people, right in the main settings ui."

The solutions offered? Kill it all with fire. I'm paraphrasing, of course.

Problem: People today change some feature then have a "broken" browser (basically, they forgot to turn it back to the default, or they didn't realize they changed it in the first place).

Solution: reset button, also notification to the user that "this page might not work correctly", some sort of an extension of how Chrome shows you that a popup and/or a cookie was blocked, based on your settings. Don't treat your users like idiots, just provide information that clears up certain odd states by explicitly informing them of something like:

"The webpage you are viewing may not work correctly because the following options differ from their default values:

1. Enable automatic loading of images. 2. Enable JavaScript.

These features of Firefox are essential for most webpages to run properly. If the webpage you are trying to access is behaving strangely or appears to be working incorrectly, <click here> to load the page with the default browser configuration."

Done, and done. No removing useful features from the browser, no treating users like morons, but now I have a new, useful, awesome, self-debugging feature which is user friendly, and doesn't require a pesky IT guru's assistance navigating the sea of 10 trillion options.

General consensus on /r/firefox seems to be in favor of it:

It's kinda ridiculous that there even was a checkbox for this in the "normal" settings.

It just provides an opportunity for the average user to shoot themselves in the foot, and people who do need this setting can almost certainly handle about:config.