Most normal users do not do this. But there might be special packages with special setups, like scripts downloading and installing from Mozillas download links. Or package creators themselves might use it. Or maybe you are a developer, in which case such direct downloads would be helpful for testing and comparing stuff. I also assume most people do not care or notice any difference with this change. Still its an improvement without much drawback and thats always good, even if its only a few people benefiting of it.
I am curious too. You tested two different versions, one beta and the other current nightly (different content). It’s okay for a quick test, but you can actually have a much closer test. Both nightly and only one day difference:
I run this quick test multiple times and on average these are typical results (don’t forget to delete the unpacked folder between each runs):
$ time tar xjf firefox-135.0a1.en-US.linux-x86_64.tar.bz2 real 0m5,784s user 0m5,700s sys 0m0,371s $ time tar xJf firefox-135.0a1.en-US.linux-x86_64.tar.xz real 0m1,699s user 0m1,621s sys 0m0,315s