Hello eggyolk, this is because websites.resistFingerprinting (https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/privacy/websites)
is disabling proper reporting of FF version in Navigator.buildID -> https://developer.mozilla.org/en-US/docs/Web/API/Navigator/buildID

However, BSP2 needs the FF version, because I make it available on FF 56 for people wanting to use it on pre-Quantum (they are not able to go to Quantum [FF57+] due to other extensions they have which wouldn't work anymore with Quantum).
And on FF56, there are some WebExtension bookmarks features not available, for which I need to activate a special code so that I can get around those lacks.

Good news however, that particular privacy setting forces buildID to a specific impossible value on Quantum (20100101) which I can recognize, and as per documentation this setting can only happen on FF 58+, so when the code sees it, it can deduce it is running on FF 58+.

*** I will get out 2.0.25 tonight so that it will work with that privacy setting and with the Privacy settings add-on, and you can get both working side by side ***

The downside is that if at some time in the future I need to recognize an FF version superior to FF58 for new features coming from FF API, I won't be able to do that for people who have enabled that setting .. And so they may not be able to benefit from those new features.

Let me know if the new version is not working in your case.