Ahh the irony of signatures lines...
1. Use the browser on your phone and visit the link.
2. Click Download
3. Click Save
4. Once download is finished, use a file browser to find the file and click on it.
5. Package installer will do the rest installing it just like a normal app
Note--Third party apps must be enabled for that to work!
Also
this post is from nearly two months ago. They're still on the same Alpha1 version. Just like earlier attempts at making firefox mobile for other OS's, they put out an alpha and then it just sits there until finally being deleted and forgotten about!