For Windows 8.1, we use a constantly developed high performing alternate browser to the well known orange "Fox", Pale Moon x64. The newest arrival (for us) with a different kind of name is SeaMonkey. It has provided a surprisingly smooth experience for us in a familiar browsing way! Think of "Explorer", one that works safely. In Windows 7 SP 1, we continue to happily browse in Firefox with nary a hiccup.
Though honorable mention goes to Opera, the performance award for a Chromium browser (on our newer system) goes to Slimjet which not only performs well, it's also kept current with frequent updates as it follows in it's Bigger Chrome brother's footsteps with a considerably lighter step!
Honestly, in my observation Opera manage to become an efficient browser without a crashes from my system nor slowdown; unlike Google Chrome from few reasons + I'm no longer at FF due to my bad experience however I'm embrace for the concept of Cyberfox and other editions.
Meanwhile Edge is my current browser which is good however bugs are present alongside of freezing of tabs.