I have problem with launching 64-bit version of 55.0.3 on Win 10 x64.
When I launch fresh install of Firefox Portable then in Process Explorer there is 32-bit "Firefox Portable" launcher process and 64-bit "Firefox" processes.
But when I move my profile in to this installation then launcher always runs 32-bit version.
How to run 64-bit Firefox with existing profile?
(AlwaysUse32Bit is set to false)
How are you 'moving your profile in to this installation'? What exact steps are you doing?
Short answer: in a proper way.
I dig deeper into this problem and definitely there is a flaw in updating routine of Firefox Portable.
Finally problem was not updated FirefoxPortable.exe - my 126.96.36.199 version from 2014 wasn't overwritten by newer 188.8.131.52 version from 2017. So probably this launcher even not know that Firefox 64 exist.
I have used Firefox Portable from a years (even before 2014) and always used Firefox Portable's built-in update option. I don't suppose that it don't update launcher itself.
That will only update Firefox itself. And then only the version of Firefox you're currently using (so if you're using the current Firefox Portable in 32-bit mode, it will only update 32-bit Firefox). It's best to update the whole thing using the PAF installer so you get updates to the launcher for bug fixes and new features like when we switched to 32-bit and 64-bit. The PortableApps.com Platform makes that easy and automatic.
Sometimes, the impossible can become possible, if you're awesome!