FYI
I installed the new firefox .paf.exe just fine, but when I attempted to execute PortableApps.comInstaller_0.91.3_English.paf.exe, I receive the following error:
The version of this file is not compatible with the version of Windows you're running. Check your computer's system information to see whether you need an x86 (32-bit) or x64 (64-bit) version of the program, and then contact the software publisher.
Your download is corrupt. Please re-download. Windows x64 shows this for 16-bit and DOS programs, which is what it mistakes corrupted downloads for. Make sure you didn't right-click on the download link (a common issue) as well.
Sometimes, the impossible can become possible, if you're awesome!
That was it. I'd attempted to download it twice when prior to the original post and got the same error both times. I just attempted the download again and received the full file, which then installed without error. Thanks.