I like Duarte's idea of making a Blend4web specific "mode"; to help eliminate cumbersome options and tools which do not apply or are unsupported for blend4web output. There could even be specific tooltips regarding which items or options work together to create desired effects.

Also, I recall in another forum topic I mentioned constraints. The response was that they are not supported at this time; but that armatures are. I think many people coming from a mechanical or architectural background; already have a good deal of experience using simple constraints. They work quite well for simple maechanical systems, such as a rudder on a wing, etc. Armatures are powerful and would seem a bit overkill for most mechanical animating.

As for this current Firefox issue, I would suspect it is a Firefox problem to remedy as opposed to a B4W workaround to be implemented.

Please keep me in mind for ideas and feedback in this area if needed.

and many costly mistakes made when a design goes out to the shop floor.

You would still export from the export menu, or if you were feeling really original instead of having a render button you would just have an "export" button which would actually just create the HTML or corresponding JSON file instead, this could respect the "output" field like other renderers do, allowing a quick explicit way to re-export to the same file. At the most this could call the default system browser on the created file if the user intended so.

eventually set the viewport to the correct "mode" to support displaying of material and texture previews as closely to the web version as possible.