The terms are very clear that they apply to Firefox the application itself (but not the source code if you compile it from scratch)

> Mozilla grants you a personal, non-exclusive license to install and use the “Executable Code" version of the Firefox web browser, which is the ready-to-run version of Firefox from an authorized source that you can open and use right away.

> These Terms only apply to the Executable Code version of Firefox

But not the source code if you compile it from scratch

> [Continuing previous quote], not the Firefox source code.

However the source code excludes DRM components, and while the terms don't mention it I believe also some API keys

> In order to play certain types of video, Firefox may download content decryption modules from third parties which may not be open source.

(It's not clear to me that these terms are currently in effect. Certainly I haven't been asked to agree to them yet).

Ah, you are totally right! They do indeed have a separate ToS for the official binaries ("Downloadable software"), see https://www.mozilla.org/en-US/about/legal/.

However, the "acceptable use" clauses that OP complains about are not part of these ToST Rather they seem to apply to Mozilla "services", which are related to Firefox accounts (https://www.mozilla.org/en-US/about/legal/terms/services/)

Side note: strangely, there is no link to https://www.mozilla.org/en-US/about/legal/acceptable-use/ on the main legal site (https://www.mozilla.org/en-US/about/legal).

The ToS has a link to the Acceptable Use Policy and says that use of Firefox must conform to it.

You are right! That's really confusing since the acceptable use clauses themselves talk about Firefox services. Their lawyers need to get their shit together.