I compared with Google Chrome. It seems that both browsers are loading the Flash widget that runs the show, retrieving the list of image URLs, and then requesting images. However, that is where things diverge. As shown in the attached screen shots, Firefox getting file not found errors when requesting the images.

Curiously, the image requests are on different addresses:

Chrome:

http://lh3.googleusercontent.com/-84R_RfLYdSg/U1-8K91Xw6I/AAAAAAAADBU/xV-d47uv_XQ/Book%252520binding.JPG

Firefox:

http://lh3.googleusercontent.com/-84R_RfLYdSg/U1-8K91Xw6I/AAAAAAAADBU/Tkbt8nplmpk/Ic42/s720/Book%252520binding.JPG

That would work without the s720/ part:

http://lh3.googleusercontent.com/-84R_RfLYdSg/U1-8K91Xw6I/AAAAAAAADBU/Tkbt8nplmpk/Ic42/Book%252520binding.JPG

If I load the RSS feed which has the image URLs, the media file links seem to be correct:

http://picasaweb.google.com/data/feed/api/user/116161407980675932364/album/SBCWorkExamples?kind=photo&alt=rss&

Something seems to be going wrong with the Flash widget reading the file and requesting the images.

Since I don't know how to read what's going on in Flash, I'm stuck at this point.

Uhh, after experimenting around with it so much, the first one seems to be working, but the second one still isn't working. Are you making changes?

Thanks for your very fast responses.

No - I haven't made any changes since sending the initial report. As far as I am aware both Photo Albums are set up identically but I'll go and check in case there is any apparent differences.

Just checked - can't see any significant difference between the 2 albums. The second one is at https://picasaweb.google.com/116161407980675932364/Rebacking

I tested in a private window, which doesn't have the benefit (cheat) of using cached version of images, and I get the same problem as originally. I don't know where that s720/ is coming from.

What's odd is, if I load the following page, I get one set of image paths, and if I then reload bypassing cache (Ctrl+Shift+r), the image paths change to the ones used in Chrome. (See screen shots) If I then reload your page, Firefox uses the cached page, and, no problems. ???

http://picasaweb.google.com/data/feed/api/user/116161407980675932364/album/SBCWorkExamples?kind=photo&alt=rss&

There are some differences between the headers sent by the Flash widget with the request for that file:

Firefox:

Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Encoding: gzip, deflate Accept-Language: en-US,en;q=0.5

Referer: http://picasaweb.google.com/s/c/bin/slideshow.swf

Cookie: _rtok=JoqB8ypLY3e3; S=photos_html=lnICBmICTJVLw5v4E4yovA

DNT: 1

Chrome (after deleting cookies, load the page, then reloading the page):

Accept: */* Accept-Encoding: gzip, deflate, sdch Accept-Language: en-US,en;q=0.8

Referer: http://www.sbookc.org.uk/our-work

Cookie:_rtok=yB0h9zjV_Lax; S=photos_html=iyFuIHjh__mHE4JnMFBo3g

X-Requested-With: ShockwaveFlash/18.0.0.209 X-Client-Data: CLK1yQEIkrbJAQiktskBCKm2yQEIwbbJAQjviMoBCJGUygEI/ZXKAQ==

Something there seems to be causing Picasa to send Firefox different paths than it sends Chrome, which may or may not be causing this problem. It's beyond me, I'm afraid.

When did this stop working?

I'm not completely sure when it stopped working. Nobody else has noticed it and reported it to me but that's not too surprising. My guess is that it's happened during the last month.

I don't understand all the technical points that you give but I assume that the bottom line is that Firefox is not going to display these albums correctly. I'll put a comment on that page to warn users.

I appreciate all your help. Does this get further escalated within Mozilla Support or should I assume it can't be fixed?

I experimented with this since unbeknownst to me Google created a Picasa album for me at some point. And it worked.

The main difference I see from yours is that the Flash widget is hosted on a different site when I generate the embed code:

Yours: http://picasaweb.google.com/s/c/bin/slideshow.swf

Mine: https://photos.gstatic.com/media/slideshow.swf

The Flash widget URL on your site actually redirects to the new one, but I suspect using the new embed tag will help. Google has these steps:

Albums

1. On "My Photos," click your album.
2. On the right, click Link to this album.
3. In "Paste HTML to embed in website," copy the HTML and paste it in the source code for your site.

Slideshows

1. Follow steps 1–2 above for Albums.
2. Select Embed Slideshow.
3. Set the slideshow settings.
4. Copy the HTML and paste it in the source code on your site.

Also see the attached screenshots. Any improvement?

Unfortunately I can't insert HTML. The 'advantage' of using Google Sites to generate my web site is that no knowledge of HTML, or exposure to it, is needed.

I'll experiment with Google Sites to see if I can find a work-around.

Maybe Google Sites needs to update its integration? The left hand and the right hand, etc.

Yes - I take the point.

But still the problem seems to be unique to Firefox and not other browsers.

A Google change breaking functionality in Firefox? This isn't the first time and probably won't be the last...

Since the image requests are generated from inside Google's SWF file, I don't have any idea how to work around this problem on Firefox's end.

OK - thanks for your help anyway.

Looks as if I'll have to warn people against using Firefox for our site.

I'll keep looking for some sort of workaround.

Could you try reinserting the slide show? Based on some threads on Google's support forum, the new place for that is:

Insert > Google+ > Photo Album

If that works in all your test browsers, then you can remove the old one.

Also, this is the Google Sites help forum if you can't make that work: https://productforums.google.com/forum/?hl=en#!forum/sites

I've just tried deleting and then re-inserting the slide show. Same problem - displays OK in IE but as a black blank in Firefox.

Thanks for the link to the new Sites help forum - I'll give that a go tomorrow, but that's enough for tonight.