it did it again today, so I've uninstalled firefox..would have told it to remove all personal data etc as a means to further troubleshoot (like we USED to be able to on older iterations of firefox but they've taken away that ability it seems) so..if it does happen again I do believe I've run the limit of steps I can take on my own, unassisted.

In case Firefox performed an automatic reset, could you check for desktop for an Old Firefox Data folder?

This article lists tools Firefox users have found helpful: Troubleshoot Firefox issues caused by malware

that was my first thought too, scans with malware bytes came up clean.

its not an automatic reset, and upon reinstalling abp and among other extensions, tab mix plus, the settings data is there, got my red page load progress bar and everything.. the browser's just forgetting the extension was even installed to begin with.

Any chance that you are using Avast 2015 as your AV application?

http://www.ghacks.net/2014/10/31/avasts-https-scanning-interferes-with-firefox-and-other-programs/

If so, run a manual update of Avast.

2014 edition still. wont be updating that today.

I just went and followed some stuff here https://support.mozilla.org/en-US/questions/1031248?utm_campaign=questions-reply&utm_medium=email&utm_source=notification

and cleared the listed files. will report back tomorrow with my progress.

attempt failed. decided to go one further and deleted my browser's profile this time.

Martin's latest article on avast! and this issue (still very mysterious):

http://www.ghacks.net/2014/11/16/latest-avast-reportedly-deleting-firefox-add-ons/

and added mozilla under app data local and roaming to the antivirus exclusions list. will advise further tomorrow on next boot.

deleted my firefox profile and uninstalled the browser cleanup feature of avast. this appears to have solved it.