I have noticed Edge being sluggish and more demanding of CPU resources than Firefox. Today, for example, I had 5 or 6 tabs open in Edge, with it being the only browser I had open, and the computer I'm using had some noticeable sluggishness in browsing and when opening other apps such as WPS Writer and WPS Spreadsheets. Granted, I had 2 tabs open for Kelley Blue Book (kbb.com) and it is a heavily tasking website. But, with Edge closed and Firefox open with 25 tabs and then opening kbb.com and obtaining a price quote on a car, I did not experience the negative impact I noticed with Edge.
I have drifted away from Firefox for periods of time but I have enjoyed using it with Windows 10. I have the latest version of Firefox, which is 42.0 at this time. During the months I've used it with Windows 10, it has consistently performed well with many tabs open and/or viewing complex web pages. One feature I like very much is being able to right click and get a popup panel with Forward and Back buttons for navigating pages. With Edge, moving the mouse pointer up to the upper left corner of the window to click the Back or Forward button is required.