Do you reboot between your attempts? Because if you first start Firefox (before using UPX) then portions of it will be in the system's cache and buffer memory (portions of your RAM that are idle and are re-routed to perform this job).
I'm well aware of these things. I'm using it since years on Windows, and believe me: I compared a lot. I also compared it with the NTFS-built-in-compression, which is also useful, but painful slow (Anyway, is at least something similar to that function under Linux?).
But as I said above ... I doubt that you will get lots of speed increase out of this. All this reminds me of old Windows programs such as "RAM Doubler" and "MagnaRAM", and such which promised to 'optimize and even double your RAM' so programs would run faster. Yeah yeah. Right. I'd rather spend my money on more RAM and super-fast SATA disks ...
UPX is not a hoax! It's just a runtime compressing tool, like many others. It's just the best and fastest. Since the programs are also much smaller after compresing, your theorie is easily disproved.
Maybe you never use Windows? But if you know the famous portable apps
http://portableapps.com/ they are already compressed with UPX by the distributors. There are also lots of programmers who use it to gain the highest possible speed, for example koolplaya
http://www.koolplaya.de is already compressed. It's used by commercial programs, too...
If you really want to have a distro where you can tune your binaries to the max: get Gentoo Linux and then set your 'build options' to optimise your binaries like mad. That should do it then for you.
That's not the same. I really like Linux, most of the time it is faster than Windows, but when I see my Windows version of Firefox starting faster
using WINE than the Linux version (and I even tried Swiftfox), than IMHO there's a design flaw.
As I said above. It would be better to spend a bit money on decent hardware (more RAM is always good) and not touch the OS's binaries.
Maybe you buy a new computer every time a program starts slowly, but I thought that's a Windows user attitude.
Besides ... Whenever you update a program package chances are that your 'optimised' binary will be replaced and overwritten again.
That's exactly the problem I'd like to get rid off.