Free web site filter add-on for Firefox (Mozilla).

I found a good, easy, and free filter add-on for the Firefox browser (versions 2 and 3), called ProCon Latte.

You can specify key words both in the body and in the URL which cause it to block a site. So if you type in the URL in the block list, that blocks the site. Plus it can block sites containing specific words. Plus it has a "white list" so you can keep some web sites unblocked.

Granted, since I haven't passworded it yet, I can unblock at will. But at least it will give me a second to remember why I don't want to waste time on other blogs.

I think Internet Explorer has built in filters based on ratings, and you can put in black-lists and white-lists too.