I was tech lead on a project that involved both Firefox and IE extension development. We tried to keep the extensions very simple, so there would be as little

I was tech lead on a project that involved both Firefox and IE extension development. We tried to keep the extensions very simple, so there would be as little to port and keep synchronized between versions. Both platforms were relatively new to us, but I don't think we were stupid. The IE plugin was about 300 times more work. Seriously, people have asked me about this a lot, and that's a pretty accurate judgment of the relative workload. Also, it's shockingly hard to find a competent COM+ developer, and the IE extension docs are actually worse than the Firefox docs, though both leave a lot to be desired. In general, installing an extension is a pretty huge barrier; don't expect users who aren't already familiar with your service to bother installing one just to try it.