Yes, it's the right forum to report issues. When you say custom fonts, do you specifically mean Typekit fonts?
In my case the issue is with Google Fonts. I have not yet had an opportunity to test typekit fonts in EA. But none of the Google fonts that I have working elsewhere appear to work on the Fire.
We just got our Kindle Fire back into the office, and someone from our team should be looking into it.
Just bumping this back up the stack to see if anyone in Adobe support experienced this Kindle Fire issue and if they have any ideas for solutions or work-arounds.