It use to work on Firefox. Not any more, but it works on IE.
I had the widget working fine on Firefox, but noticed I just get the twitter widget box with "Join the conversation" and nothing else.
I went and created new source code (I noticed it changed since I last created the code), copied, pasted, and even corrected the missing "http:" in the source code as discussed in other threads here.
That just shows "Tweets by @CamLaversDesign" and nothing else.
I have since noticed it works when I use IE.
See the results in the old style code here: http://peppermills.ca/about.htm
and the new style code here: http://peppermills.ca/testimonials.htm
Again, if you use IE it works, but doesn't if you use FireFox