Best web browser for older Mac

I have a 2013 Mac that is running Sierra 10.12.6. Safari was working fine until a couple months ago, now I am running into issues where I can't use certain sites and can't watch videos. I have google chrome but it makes my computer slow and I just got a notice that I will no longer be able to update it with 10.12.6. So my question is what is the best web browser I can use with my older Mac? I would like for it to be free, secure, fast and not use a lot of memory as I usually have multiple tabs open at one time. if it comes with a good bookmark manager that would also be a plus. I see that I can download older versions of certain browsers, but I read that this is not a good idea since the updates are necessary for security purposes. It is becoming increasingly difficult for me to conduct basic research so any sites you can refer me to with this info or help you can offer would be much appreciated, thanks!