Hi Christian,
Summary
I've done some reading on this and some testing, and I'm 99% certain that v65 of Firefox scheduled for release on 29th Jan 2019 will block, by default, Adobe DTM (and, therefore, all Digital Analytics and Marketing tags that an organisation delivers using DTM).
My reasoning is below; I would be very grateful if someone is able to tell me that I my conclusions are incorrect.
In summary, my conclusions are:
- Firefox v65 will block Adobe DTM by default (and all content delivered by it)
- Firefox v65 will block calls to Adobe Analytics (and other Digital Analytics tools) by default
- To circumvent blocking of Adobe DTM-delivered content, an organisation must host the DTM file(s) on their own web content server
- To circumvent blocking Digital Analytics server calls to *.omtrdc.net (the Adobe Analytics data collection centres), an organisation must have a CNAME redirect (e.g., metrics.myorganisation.com --> mycompany.d3.omtrdc.net)
- Adobe Target will not function under Firefox v65 by default
Content Blocking in Firefox
Firefox v63
Default Settings
The screenshot below shows the default setting in the current release of Firefox.
The "All Detected Trackers | Only in private windows" setting will block all tracking and marketing in Private Browsing; e.g., Adobe DTM, Google Tag Manager, Adobe Analytics, Google Analytics, Adobe Target, Facebook

Results
With the setting demonstrated above, there are no problems with Digital Analytics and Marketing tags (including Tag Management Solutions) in "normal" (i.e. non-Private) browsing.
Firefox v65
NOTE: in the blog posts and reporting around the new "Enhanced Tracking Protection" features, the specific version number is not often mentioned - the phrase "early 2019" or "January 2019" is used; the only release that fits these descriptions is v65.
Default Settings
The change that is anticipated is highlighted in the screenshot below:

Results
Enabling this setting immediately modifies how pages will load when instrumented with some examples of a Tag Management Solution (TMS), Digital Analytics tool, or Marketing tag.
Instrumented with Adobe DTM, Google DTM, OneTag, Adobe Analytics (using a CNAME redirect), Google Analytics, Adobe Target, Boldchat, and so on - none of it gets through

Instrumented with Tealium IQ and Adobe Analytics (using a CNAME redirect) - both of them are loaded and functioning

Additional Considerations
- Adobe DTM can be deployed from an organisation's own infrastructure
- Any library (e.g., Adobe Analytics, Google Analytics) can likewise be loaded from an organisation's own infrastructure
- However, server calls going to Adobe Analytics data collection centres (if it is implemented without a CNAME redirect) will be blocked
References
Latest Firefox Rolls Out Enhanced Tracking Protection
Firefox Release Calendar - MozillaWiki
How does Firefox choose what to block?
Adobe DTM hosting options