For several years I've been wanting to make the switch to Chrome from Firefox, but the lack of a couple of key plugins has held me back. One of these was the way that windowed plugins were handled initially (the popup for LastPass in Chrome was hideous, but that's no longer an issue.)
The bigger issue for me was the lack of a good vertical tabs plugin for Chrome. I've tried several tabs but none of them seem to work the way I've gotten used to with the venerable Tree Style Tabs in Firefox.
Enter, Vivaldi. This is a Chromium-based browser that offers a lot in terms of UI customization over the stock Chrome implementation.
With tab handling in particular there's a lot to like about Vivaldi. The vertical tab bar allows you to take advantage of the vast amount of horizontal real estate modern wide-screen monitors provide. By placing your Windows Taskbar or MacOS Dock on one edge of the screen and your browser tabs on the other you give yourself the maximum amount of vertical space for your browser to display content.
Vivaldi also offers "tiled" tabs which give a much larger surface area and a live preview of tab content. This is useful for quickly locating what you need in a more visual way.
The biggest drawback to Vivaldi compared to its more established counterparts is the lack of synchronization for settings and extensions. Not being able to quickly establish the same browser environment across multiple machines (never mind mobile) is a pretty substantial stumbling block. Add to that the lack of a mobile browser and the platform just seems incomplete.
I really enjoyed using Vivaldi for the time that I had it installed. Being able to take advantage of Chrome/Chromium features was a big plus, but ultimately the lack of a good sync option was a deal breaker for me and I've had to return to using Firefox for the time being.