Unfortunately, limiting the number of open tabs is often a poor way to approximate the resource utilization of those tabs. A lightweight tab might use 5mb and ~0 CPU while a heavy-weight one might use 1.5gb and 50% of your CPUs.
For what it's worth, you can write browser extensions that limit the number of open tabs, but these wouldn't get around the base issue, and they introduce a lot of complexity (Should a user lose work if it would result in creating a new tab?)
I fully understand your concern and until I got my latest system, this was always an issue for me as I just kept opening new tabs going from one subject and then extensions of that subject and suddenly I was locked. When I got my new system, I spent all I could on memory and hard drive space. Now I save nothing except programming on my hard drive, and save all my data on an external hard drive of the same size. I also really loaded up on memory. Now I might have 20 or 30 tabs open and running with several Excel and Word windows open, gathering data, copying and pasting data and so forth. So I think the real answer is memory and hard drive space. I have never experienced a lock up in my new system, by the way.