Which IE8 had around the same time (It may have launched after Chrome, but in the contemporaneous betas, they both had the feature)
What made people switch was a combination of everything google did having the sheen of "cool" around it, and the fact that I.E development was slow and shoddy.
I think that's when Google noticed that the IE monopoly was breaking, and they jumped onboard and took Konqueror's code and then launched their own browser. The same code that Apple used for Safari. So they basically came in on the hard work of Firefox and the KHTML team and took over the market by putting Chrome right on Google's homepage.
It's my opinion that Chrome didn't become popular because it was better, or because it was cool (no average user cares about that). It became popular by being right there on everybody's home page, right at the perfect time that people were catching on to the fact that IE had zero security.
Firefox broke the monopoly and freed us, and then Google and Apple came in and shat all over them.
The first time I saw break away tabs in Safari for Windows in 2007. Before Chrome was introduced.
Safari 3
https://lifehacker.com/safari-3-beta-now-available-for-windo...
Safari 5 http://cdn.osxdaily.com/wp-content/uploads/2017/08/safari-fo...
The safari 5 screenshot you have is EDGE with a safari installer in front of it.
In addition I also consider the marketing reach and the success of Android as important. Fwiw I never switched completely to chrome and quite regularly got a hint to try out a better/optimised browser.
Process sep per tab was a Chrome feature. Unless you count Lynx and separate instances per browser page ;-)
But the major improvement that made everyone switch was process separation for each tab. One tab could crash while the others stayed functional and a security vulnerability in one tab would have a more difficult time compromising the others.
It's also one of the reasons Chome uses so much memory, they failed to keep optimizing their copy-on-write paging behaviour so that tabs would share more memory among themselves.
Nowadays Firefox has process separation for tabs AND it's not written by an advertising company, so I like it better.