Hi Anne
Firstly that sounds like a very old version of Firefox are you sure that is what you are using? e.g. Click the menu button, click Help and select About Firefox. The About Firefox window will appear. The version number is listed underneath the Firefox name. See release history
www.mozilla.org/en-US/firefox/releases/
But anyway open the developer tools (F12 or Right Click > Inspect) and view the console tab - what error(s) do you see?
Have you cleared offline files?
What happens if you use a new private window (Ctrl + Shift + P)?
Do you get the same problem with all your LOs or is it LO specific?
Can you share a link to an LO that demonstrates the issue? That said, even with a link, if the issue is browser version related it's unlikely any of us will still have that old a version installed.
HTH
Ron