Themes suddenly stopped working after trying new theme

Question

I installed a theme in TB and it looked nice, so I decided to try it in FF36.04. It worked, but when I tried to go back to my old theme (Same author), it didn't work and the area at the top went black with just the usual text. I tried to go back to my old theme (same Author) which has worked fine for years. When I went to Add-ons | themes it lists the various themes, but doesn't display pics. If you go to the specific page of the theme (via add-ons) it only shows the author and theme name along with the disable/remove button, no picture or any other details. This is the same for all themes.
I tried adding a new theme at random and it worked and displayed the picture in the themes tab, but the others still don't work. They show different colours if I enable different themes, which I assume is the background. I've tried all the usual things, going back to default (seems OK), tried restarting FF, Rebooting laptop, etc. but nothing gets my old theme back that I've had for years.
Because a new theme worked, I could presumably remove all my old themes and go and download them and install them again, but something went wrong and I'd like to fix whatever it is, rather than perhaps leave a hidden problem.
Any suggestions?
***Edit - Just updated to FF37.0.1 and no change. I have noticed though that the theme I tried to add originally (the one when the problem started) is not actually in the list of themes! It did work at first, it was when I went to change back to my old theme that the problem started.
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Answer 1

A bit more information.
I found the lightweighttheme-header and lightweighttheme-footer would change to HTML files if I set the default FF theme. I renamed those for safe keeping and copied the picture files of the same name from TB, which I confirmed were the correct pictures.
Restarted FF and no change (tried changing personas, etc). It did not create a lwthemes directory. I copied the 2 files from the lwthemes directory of TB over to a new lwthemes under FF's xxxxx.default and started FF again, but still no change.
I checked the prefs.js and found the 'A Tropical State of Mind' referenced in numerous places, along with other personas. Also found these settings -
user_pref("lightweightThemes.isThemeSelected", true);
user_pref("lightweightThemes.persisted.footerURL", false);
user_pref("lightweightThemes.persisted.headerURL", false);
user_pref("lightweightThemes.usedThemes", "[{\"id\":\"360804\",\"name\":\"A TROPICAL STATE OF MIND\",\"headerURL\":\"https://addons.mozilla.org/_files/277332/atropicalattitudeofmind.jpg?1296426260\",\"footerURL\":\"https://addons.mozilla.org/_files/277332/atropicalattitudeofmindF.jpg?1296426260\",\"textcolor\":\"#000000\",\"iconURL\":\"https://addons.mozilla.org/_files/277332/preview_small.jpg?1296426260\",\"previewURL\":\"https://addons.mozilla.org/_files/277332/preview.jpg?1296426260\",\"author\":\"ÔÿàSaSSyGirLÔÿà\",\"updateURL\":\"https://versioncheck.addons.mozilla.org/en-US/themes/update-check/360804?src=gp\",\"version\":\"0\"},{\"id\":\"277395\",\"name\":\"COLORFUL HONG KONG\",\"headerURL\":\"http://getpersonas-cdn.mozilla.net/static/9/5/277395/HK.JPG?1321450621\",\"footerURL
......Goes on with other personas
I changed the '''lightweightThemes.persisted.footerURL''' and headerURL to true and I now have the correct pictures back in FF - However when I go to the ad-ons | Appearance, the list of personas still has no pictures and the individual pages for those personas are the same (blank other than the name and buttons), even the 'A tropical state of mind' one that is now showing correctly at the top of FF. It has updated the files in the lwthemes directory.
I then tried to select another persona with no picture and it's now back to the same problem with just the background (presumably) up, even when changing back to the tropical one that was just working.