There is no indication that they’re blocking adblockers or taking away firefox customization.

Yet.

We don't know that after they are deeper and deeper into the advertising industry, that they don't just go ahead and do it.

Remember how Google wasn't always evil? Money changes companies (and people). Advertising money could very well change Mozilla. Plus, remember, these statements are them telling you the public version, things that they are claiming will happen. Often times what goes on behind the scenes is very different.

I don't think it's unreasonable to be concerned by this.