you may not even have to change to another browser or fork, please have a look at some designs in https://trickypr.github.io/FirefoxCSS-Store.github.io/ select a design and follow the page, and you shall find the instructions (usually just downloading/pasting userChrome/Content.css)

and for scrolling tabs, if your problem is very small tab size, then try changing browser.tabs.tabMinWidth in about:config

Floorp, I use it and I love it. It's especially great for Opera refugees, it has workspaces and stuff. Soon Firefox will support tab groups natively, and then Floorp will be perfect. It's a Firefox fork though.