I'm a little worried about the terms of the agreement not being disclosed. We're launching a search ad blocker that removes all but one ad per page on Google. Bing, and Yahoo search results. We're trying to re-introduce the idea that most of the screen space should be content, not ads, and we put some teeth into that idea with ad blockers. (Yes, you can block all the search ads if you want.)
I used to work for Mozilla. One thing I can say with confidence is that Mozilla would not have signed this agreement if it restricted their freedom in such a way that they'd start blocking ad blockers or other plugins. Mozilla is very much focused on user control, and is not going to let a third party restrict what a user can do with their software. Google and Mozilla have definitely not always agreed in the past, and I'm sure Mozilla will continue doing things that it believes are in the end-user's best interest. Keep in mind that Mozilla introduced the Do-Not-Track http header, which which Google (last I knew anyway) still hasn't added to Chrome.