Lately I've had some requests to enable using Mozilla inside FeedDemon, and I'd like to address this here. The short answer is that I would like to include Mozilla as an option, but past experience with TopStyle has taught me that it's too much of a support burden. Now the long answer...
TopStyle was one of the first (if not the first) commercial products to embed Mozilla's "Gecko" rendering engine, which enabled viewing web pages side-by-side in IE and Mozilla (see this page for a screenshot of this feature in action). TopStyle relies on Adam Locke's Mozilla ActiveX control for this feature, and he should be commended for the great job he's done. My rant here isn't about Adam's excellent work, but instead about the poor way in which this control is included with Mozilla.
Even though this ActiveX control is installed with Mozilla, it's not registered, which means that it doesn't exist as far as Windows is concerned. I couldn't have TopStyle automatically register it since the steps to do so have changed considerably over time, so customers have had to register it themselves.
As visitors to my newsgroups can attest, there have been countless support questions from people trying to get Mozilla to work inside TopStyle. All too often, the problem is due to changes in the latest Mozilla build which renders it inoperable inside TopStyle (as well as inside other programs which support Mozilla, such as HomeSite). Mozilla 1.4 builds were a good example - not only was the control moved, but it also required downloading a "supplemental zip file" to get it to work. And I used to own a computer on which TopStyle's Mozilla preview never worked after I installed a new Mozilla build. If I can't figure it out, how can I expect my customers to? They have better things to do.
TopStyle is a web authoring tool, so I can accept the additional support burden since web authors need an easy way to check their work in different browsers. FeedDemon, on the other hand, is an RSS reader, so offering Mozilla as an internal previewer doesn't justify the support costs.
My hope is that the Mozilla team will realize the importance of the ActiveX control and take care of these issues so that developers such as myself can rely on it. As it stands now, though, FeedDemon will have to rely solely on Internet Explorer for internal previewing.
PS: Just in case you were wondering, other browsers - such as Opera - can't be embedded in software the way that Mozilla and IE can.