IE7 did have tabs. In fact, it was one of the main features. They didn't make significant standards compatibility improvements until IE8, and only really in IE9. IE10 was the first one (since 6) to actually be comparable to other modern browsers.

IE8 was also the first IE to address a lot of the memory leaks that older versions had. DOM <-> JS access was referenced via COM interfaces and out of scope cleanup didn't cross bounds in earlier versions.

IE8 did have a really bad bug around the JSON.parse implementation though.

Oh, it had a JSON bug? The fact it supported JSON was one of my favourite parts :(

If you modified the Object.prototype or Array.prototype (which was common at the type with libraries like PrototypeJS) and used a rehydration function with JSON.parse, the runtime would throw an error you couldn't catch, and stop JS functioning. In IE 8.x ... almost worse, the JSON.parse function was locked... I wound up using a wrapper JSON.parse2 or something that was the JSON library edited to attach to parse2 for IE8, other browsers would alias parse as parse2.

I then used the parse2 in everything at that time. In the end, it sucked and I'm glad I don't have to do it anymore. IE8's quirks were what I would consider the last bad version of IE... since then it's been mostly okay on release, but ages rapidly, but enough turnover that you aren't on it too long. Until current IE11 as it's tied to windows releases, and some people/orgs didn't upgrade.

IE7 did have tabs. https://en.wikipedia.org/wiki/Internet_Explorer_7

Yeah, but the effect of the banner on the graphs of each was sharp and immediate.

The graph is measuring in six month intervals, so the March 2009 release of IE 8 needs to also be considered.

It's not measuring in six month intervals, that's just the scale at the bottom. There are peaks and troughs that are very clearly higher resolution than that.

IE7 had tabs.