I’m on FaceBook a lot, since I play online games. I know, it’s a stupid waste of time, but I like it. When you play a lot, BetterFaceBook is an add-on you can’t miss. But for some reason, I could not install the latest version in Chrome. I had 4.5 installed, but 5 would not install because of an “invalid crx header” error. Even when downloading the file and opening it in Chrome, it would give the same error.
So I unpacked the CRX (it’s basically just a ZIP-file) and installed it via “Load unpacked extension”. That worked. Not sure why Chrome did not like the crx, but I thought this might be of some help to you.