I had no idea why this was happening! Firefox's native debugger provided no clue as to what this was. I found the same symptom in your demos and was able to locate the code that affected it.
I very much thank you and your team for the great support! Explaining this saves me many more hours of frustration, and provides a much better understanding of this amazing new tool.

I think I'd prefer to tweak my css, rather than write more code.

Yes, Firefox. I encountered this issue with version 35, but it I upgraded to 38.0.5 and still have the issue. I also updated my Nvidia driver with no effect.

This drove me crazy, but I think I located the issue. Here is a typical “exports.init”, using “app.init”:

exports.init = function() {
m_app.init({
canvas_container_id: "canvas3d",
callback: init_cb,
show_fps: true,
physics_enabled: false,
alpha: true
});
}

If the above function is used, the scene loads clean. If “alpha:” is false, then a black box appears in the upper left corner of the screen, during the scene loading. Why? Is this a bug?

This doesn't affect the main scene, once loaded, but looks bad when presenting a nice preloader. I may be able to just live with “alpha” kept as true, but I hope you may comment.
This “black box” issue also appears in earlier versions of B4W. It is strange that I haven't noticed it, before, but I am just now getting involved with pre-loaders.

The “Code Snippets” example shows this symptom with:
Custom Anchors
Dynamic Geometry
Instancing

By the way, “Morphing” (in Code Snippets)doesn't work for me, in the 15.06RC.

My system:

Windows 7 Pro
I7 Cpu w/24Gb ram
Nvidia Titan Black GPU
Blend4web 15.06RC

Thanks

Sorry!

It is embarrassing to get caught on such a dumb mistake. My main project started a few versions ago, and although I kept updating the Blender addon, I forgot to use the latest version of b4w.full.min.js . I apologize for troubling you with my error.

This zipped package exhibits the annotation problem I am experiencing. The short description field does not display.
I am using Firefox version 35 with Windows 7. I have also reinstalled Blender 2.74 and B4W 15.05.

I just created a new .json file, from a fresh Blender scene, and the 15.5 developer plugin.
The annotations with the short description field will still not display.

I have been adding Anchors/Annotations to my project, and would like to have comments and suggestions made on a couple points.

1. “Detect Visibility” does sort of hide the Annotation when something obstructs it, in the foreground, but not completely. I would prefer to be able to make the annotation completely invisible, if possible. How might I do this?
2. Annotations have “Title”, “Category”, and “Description” fields. Very short descriptions (like a date or printed number) will not appear, unless the description has substantially longer character count than the title. The description field will just appear blank, in these cases. For example, and annotation with a title of “XX” and a description of “XXXX” will display the title but the description field will appear blank. Am I doing something wrong?

Thank You, Roman!

I was close! I understood that Blender's NLA feature was key to the simplest method to get animated transparency. The only example I could find was here:
https://www.blend4web.com/media/uploads/0234c4e7-bc3f-44d7-9840-6ba6d0b3ecc4/alpha_NLA_test.blend
https://www.blend4web.com/media/uploads/cb508bce-8b12-4071-83bd-372207964900/alpha_NLA_test.html

This earlier example used game engine features, rather than a javascript app to drive the animation. You have just provided the first javascript example, I can see, for doing this.

I am still studying the code, but I can see that my example is there, and clear enough to understand!

I believe your "code_snippets" example, in the distribution, is very helpful in understanding how features work, and provides an excellent way to provide support and explanation on specific problems, like the one you have just answered. The "Christmas Card" helped me to get started with Blend4Web, but it took time to discover which parts of the code affected what features. The "code_snippets" offer bare bones examples of individual features with only the minimum code needed to make the example work. I look forward to seeing more examples, like this, in the future.

My project is stalled over the following problem:

The “code_snippets” demo includes an example of procedural camera animation. This feature is perfect for my needs, except that I also wish to have a plane object, containing an image, fade in after the camera animation completes. In other words, I want the viewer to explore my scene, click an object, sail into a targeted point of view, and watch an image gently fade in.

I am weak on both javascript and Blender's gaming features. Is anyone interested in suggesting how an alpha transparency “fade in” may be performed after completing a procedural animation in the “pear and apple” code_snippets example?

I have experienced a similar crash, with Firefox
Windows 7
Firefox 35.0
Intel I7
Nvidia Titan Black