Bottom line: Safari seems to run faster and better than Firefox and Chrome.
I have been happily using Chrome on my early 2014 MacBook Air with 8GB of memory since... well, for years before I had this particular Mac.
Then all of a sudden maybe a month ago my M a c s t a r t e d s l o w i n g d o w n . . . a L O T . I would restart it and it would be better... for a few hours.
And I'm not talking "laggy," I'm talking seriously slow. One morning, I tried actually closing the apps I had open rather than forcing a restart. It took about an hour. It was so bad that it seemed to be clearly more than "you are running too many apps." My main suspect was VMWare Fusion, since I'd recently upgraded the OS to Windows 10, and Fusion itself. In the process of troubleshooting, however, I discovered that it was all Chrome. As soon as I would force-quit Chrome, things would speed up within moments.
The diagnosis was slightly complicated by the fact that Activity Monitor would run so slowly that it wouldn't update, so you couldn't tell who was hogging all the cycles. When I would force-quit chrome, it would suddenly do about a hundred updates all in a row. [Before force-quitting, it would update only a tiny bit... it was strange to see Activity Monitor listing itself as "Activity Monitor (not responding)."]
So I haven't really liked Safari ever since the days when Apple locked you into their own search engine, because it was a profit center for them. That was, uh, a while ago. Also I love OneTab, and Chrome doesn't have it.
So the next stop was Firefox (which does have OneTab), which I use on my Windows VM. It was OK, but response was noticeably slower than Chrome when Chrome was running well.
On to Safari. First I had to upgrade to El Capitan, because the new (OK, new to me) Safari allows you to "pin" tabs, and to mute browser windows, both of which are great features. Happily, that was painless. I'd been meaning to do it anyway, because once Apple goes to their next OS it will be impossible, and the new OS typically breaks a lot of stuff, so I try to upgrade after most of the kinks are worked out.
Bottom line: Safari is working great. It is at least as responsive as Chrome and generally my Mac seems to be running faster and happier than it has in a very long time. And there's an extension called Sessions that seems similar to OneTab, though it is not currently being supported, :-(
