I rarely feel like the slowness of a website was due to the browser. I mean .4 seconds or .5 seconds does it really matter? I've been using Firefox since it was Firebird and speed has never really been a complaint. People need to measure and quantify everything.
What appeals to me about Firefox is how customizable it is, and all the extensions.
On old HW it does matter. I use X220 Thinkpad, it's still fast using chrome, and slow using firefox. But since 115, it's noticeably fast... so... it matter, for me.