Firefox doesn't make any configuration changes at Windows startup, although its background service may check for updates.

There are other programs that may do a little browser cleanup at Windows startup, including CCleaner. I haven't previously heard of losing extensions, but if you use CCleaner or a similar browser privacy tool, you might want to try deactivating it as a test to see whether that works around this issue.

I have CCleaner,but run it manually at irregular intervals.I haven't used it in a month or more.

different extensions but the exact same symptoms as original poster.

Hi XRaiderV18, do you have any privacy or utility software that may run at Windows startup and clean up browser settings? In addition to looking at CCleaner, I also would check Advanced SystemCare or similar utilities.

Similar symptoms in this thread: https://support.mozilla.org/questions/1031221 (unsolved)

the only utility software that runs at startup is my antivirus, and with regards to ccleaner, I'd need a professional who knows what they're doing to look it over.

Hi XRaiderV18, do you mind mentioning your brand of antivirus software? The sudden appearance of this issue could be a new "feature".

Regarding CCleaner, if you are not running it, then please ignore that part. (It has settings to clean up browser data such as history and cookies when you reboot Windows.)

There appears to be some connection to avast! (why/how still unclear):

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

After reading that article and all the comments, it ends with a post by Lukas (of avast!, I assume) saying:

"The Browser Cleanup team is now working on a fix, which will be delivered via a VPS update shortly (tomorrow)."

So that's promising!

Excellent detective work! I DID recently update FF and am running the free version of Avast! Just unchecked Browser Cleanup as well.

I stole the link from another thread, but I'll take credit for updating this one. ;-)

I don't care where you got it from if it solves my problem.Thanks kindly for your efforts!

avast and I've just turned off the browser cleanup tool

See also the post by Lukor in the second link:

• Avast suddenly doesn't like several Firefox add ons:
  **https://forum.avast.com/index.php?topic=160289.0
  **Lukor: https://forum.avast.com/index.php?topic=160289.msg1152011#msg1152011

deleted my profile, set everything back up, uninstalled the browser cleaner function on avast. seems stable..will advise further at next restart tomorrow morning.

Thanks for resolving my issue! I just booted the computer,and my add-ons are still there!