See:

• https://support.mozilla.org/kb/share-your-screen-firefox-hello

I already read that article but neither I or my husband have the option on the right to share tabs because that icon is not there. Firefox says I have the latest version.

Yes, it looks that screen sharing is disabled in the Firefox 38 release because of known issues.

• bug 1155195 - Please disable screen sharing for 38

Please do not comment in bug reports
https://bugzilla.mozilla.org/page.cgi?id=etiquette.html

Ttriciaa said

I'm using firefox version 38.0.5. Is screen sharing available on Firefox Hello yet? It doesn't show up on my conversations.

Thank you very much.