You can change when the overflow scrolling starts by setting browser.tabs.tabMinWidth to 50 (or any number you want, the unit is pixels) in about:config
One sec let me try to explain how to do this to my grandma who is currently x thousand miles away. Oh yea and if something breaks good thing I'm there for tech support amirite.
Oh she doesn't. The issue Grandma, Uncle Fat, Cousin Lou all have is they used this thing and started getting used to it and then they got an update and someone changed everything and they don't know how to do anything anymore. Repeat this three or more times and when you tell them to use something they smile at you and nod then stick with Chrome because it's something they know how to use and doesn't change all the time.
Your claim is FF updated something and your Grandma couldn't figure out how to do anything? Which update was this?