All the other methods will not work, because...
...Mozilla (and all other major browsers, as pointed out in paislee's comment) has this thing called the "Same Origin Policy" which states:
The same origin policy prevents a document or script loaded from one
origin from getting or setting properties of a document from another
origin.
Essentially, Mozilla makes sure you cannot access another webpage's properties thru JavaScript because that would be a security hazard (for cookie hijacking and such I believe).
For example, here was a similar question when discussing an iframe for a page of the same origin; here is the answer as applied to your problem. As you can see in Firefox's error console, your "permission denied to access property document"...
Ok, so you have a couple of options now that you know you can't access the iframe's height thru JavaScript (because it is hosted on another domain):
- Change it so you do control the contents of the iframe (then either put it under the same domain or use the solution posted in the similar question).
Assuming 1 is not possible you have to use your server to access the webpage. The first option here would be to screen scrape the contents of the iFrame and then display it
- If you aren't up for writing a screen scraper you could use a proxy script and then display an iframe of your proxy (hosted on the same server); this would permit you to access the site as if it we're your own and the user would notice no difference (Note: I'm pretty sure this is against all terms of service/possibly illegal as the user could try to interact with the website (unaware it is loaded thru a proxy) in the iframe (i.e. login)... and you would effectively be phishing)
I am assuming that what is loaded in the iframe is a set of comments (IDs kind of gave it away), and I will also take the liberty of assuming each comment has a fixed height or maximum height. In which case you could write a php script that loads the page, counts the amount of comments (regex) and then multiplies number that by comment height to determine the appropriate height of the iframe
Good luck,