Hold on! I have at least a partial solution. Forgot this because it's been so long since I used it, but if you type something into the address bar that's in the webpage title or url, it shows up in the pop-down as an option to switch to that tab. Still, being being able to search for any text in the open tabs would be a useful addition.

Yes, just use % somewhere in the location bar, maybe before you start typing the info unique to the tab you are looking for.

• see Address bar autocomplete suggestions in Firefox_changing-results-on-the-fly

Check out FindBar Tweak from the Mozilla Add-ons Web Page. There’s a lot of good stuff here.

This doesn't seem to work. At least not for what I'm wanting to do. It seems that using the % in the search yields the same results as you get without the % - i.e., it finds that search term in the page title, but not in the page text. I used a known open tab and typed, "% amboy" into the location bar. That just takes me to a web search for "% amboy." To make sure I'm being clear, amboy is a word in a known open tab.

Fred's answer does it! From one Fred to another, Thank you, Fred!  :-)

Glad to be of service.