https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save Note: Some software, like Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

FredMcD said

https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save Note: Some software, like Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

I don't have any software like that installed. Plus, I am using Mozilla on Linux, Windows 8 and Windows 10. The behavior is exactly the same across all platforms. The setting never sticks past one session.

That is a part of "Firefox Share" services. https://support.mozilla.org/en-US/kb/share-webpage-through-firefox-share

Sorry, I can't provide more specific information about how that works - I am decidedly anti-social [networking, that is] and have never tried to use that new feature. From the little I have read when that feature was new, besides "Click on a service to add it to Firefox" I think you may need to be logged in to each network that you want to "share on" for that service to work - that may be the "enabler".

Being logged in to Facebook or whatever makes no difference. Share on Facebook never sticks beyond the session where I enabled it. Send page by GMail never sticks beyond the session where I enabled it. None of it works beyond the session where I enable it. Everything else handled by Sync works fine and add-ons all function just fine. I don't have any evidence that this feature works beyond one session.

I have the same issue on Windows 8. Facebook and gmail are my homepages and I use a master password, so as soon as I've started a Firefox session, I'm logged on to Facebook. However, when I click the paper plane for the first time in a session, I have to go to the "share services" page to "activate". :(