Rated 4 out of 5 stars

Nice and simple and I can get it to work with Firefox3 using Nightly Tester Tools.

One problem, S3 Buckets are case sensitive, URLs are not, so if you have a mixed case bucket name e.g. MyBucket, this will not be resolved by s3://

This review is for a previous version of the add-on (0.03). 

This has been fixed

s3://MyBucket works now - thanks for the report