Timely with some of my own posts, Firefox posted on X for the first time since Jan 2025:

We took time off of X, but we’re back. The internet is changing again, so we’re here as an independent voice for our users and the open internet.

Mozilla never stopped posting on their own separate account. I feel like “the internet is changing again” could use a link to a longer blog post. I assume that’s partly about AI, and most AI people are still only on X.