My experience with Firefox got much faster after I installed a local DNSMasq server.
Things got noticeably faster after that point.
For details, see: https://news.ycombinator.com/item?id=21877330
This comment was when I first installed DNSMasq on a very low powered OrangePi Zero (512MB) on home network. I worked a lot of kinks and this situation holds truer when compared to that time.
For instance, running the Jetstream2 and Speedometer2 tests on https://browserbench.org on Mac OS M1 CPU and Windows 10 Ryzen 3700:
Mac OS M1: Jetstream2 Firefox score of 115. Safari score of 227. Speedometer 2 Firefox score of 203. Safari score of 218.
Windows 10 Ryzen 3700: Jetstream2 Firefox score of 92. MS Edge score of 145. Speedometer 2 Firefox score of 95. MS Edge score of 142.
These are bare metal installs running off the same connection method to the same network. I understand what you are saying about DNSMasq, but I wanted to test out the "seems" portion of his comment. If Firefox seems slower on any particular machine, that is because it is.
Since I mainly use Linux (80%) and Mac (20%), I sometimes think that everyone is using the same OS with me.
You're right, I didn't think of OS dependent performance difference.
The aim here is to minimize the DNS query turnaround time and reduce the latencies while opening a connection.
When the network is working smoother, Firefox's performance goes up in a disproportional fashion. I didn't notice the same amount of improvement in other network bound stuff but, Firefox went from "meh" to "youjustdidwhat!?" after DNSMasq installation and modem change.
Same thing also happened when I changed my modem 7-8 years ago after my venerable Alcatel Speedtouch died.
So, in retrospect, modem chipset really plays a central role in your home network performance.