Are you logged in as the Admin/Owner?

This can happen if there is a problem with the extensions.json file or the prefs.js file in the profile folder.

Do you have cleanup software that might affect files in the hiden profile folder?

Location used for the main profile that keeps your personal data in "AppData\Roaming" (Root Directory on about:profiles).

• C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>\

There is software like Advanced SystemCare with its Surfing Protection feature that can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

WestEnd said

Are you logged in as the Admin/Owner?

Yes.

Where you download that theme from? Mine doesn't show those?

The currently selected theme is stored as the first theme in this pref that you can find on the about:config page.

• lightweightThemes.selectedThemeID = 1
• lightweightThemes.usedThemes = {JSON data}

If you do not keep the value of this pref then Firefox will fallback to the default theme.

• https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• http://kb.mozillazine.org/about:config

cor-el said

The currently selected theme is stored as the first theme in this pref that you can find on the about:config page.

• lightweightThemes.selectedThemeID = 1
• lightweightThemes.usedThemes = {JSON data}

If you do not keep the value of this pref then Firefox will fallback to the default theme.

• https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

You can open the about:config page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue.

• http://kb.mozillazine.org/about:config

The place where you have {JSON data} is just a pair of square brackets. I'm betting that's where the boggle is....Now, I just need to know what to put there!

I am having the exact same problem. I also have the square bracket problem. My prefs are:

   lightweightThemes.selectedThemeID = <blank>
   lightweightThemes.usedThemes = []

Is the value 1 required for selectedThemeID? How can we figure out what to put in for the JSON data?

This means that not themes are installed and selected because otherwise selectedThemeID and usedThemes would have a not-blank value.

• lightweightThemes.selectedThemeID = <blank>
• lightweightThemes.usedThemes = []

JSON data uses curly brackets with key:name pairs ({"key":"value"}) for its data. The enclosing square brackets are required because this pref can be an array of comma separated lightweight themes: [{<theme-1>},{<theme-2>}].

• https://en.wikipedia.org/wiki/JSON

You can install and enable a theme to see what this JSON data looks like.

[{"id":"1","name":"Unknown","headerURL":"https://addons.cdn.mozilla.net/","footerURL":"https://addons.cdn.mozilla.net/","textcolor":"#","accentcolor":"#","iconURL":"","previewURL":"","author":"Unknown","updateURL":"","version":"1.0","updateDate":"","installDate":""}]

That actually helped me find the dratted prefs.JSON file. It was in the "Weave" folder, in the subfolder "Failed." From that, I took a wild guess that something went wrong with it between the last two updates. I copied my bookmarks backup folder out to the desktop, just in casepulled a reinstall and ran the firefox refresh twice, till it showed only the default theme (It had been flashing mine up for the few moments before firefox was fully started, only to have it vanish as soon as it had.) and then reinstalled my themes from their pages.

All seems to be working fine at the moment. Selected my theme, closed firefox, wated a few, then reopened it, and my theme was still there!

Note that the Weave folder is part of Sync (Sync was formerly name Weave), so it is possible that Sync was interfering.

cor-el said

Note that the Weave folder is part of Sync (Sync was formerly name Weave), so it is possible that Sync was interfering.

So, for others having this issue, just deleting the weave folder might work?

I wouldn't know whether deleting this folder helps, this folder merely stores data that is used by Sync. It is possible that for some reason there is some sticky Sync data stored in the folder and syncing preferences is enabled. Themes are part of Sync:

• about:config ->
  services.sync.prefs.sync.lightweightThemes.usedThemes = true
  services.sync.prefs.sync.lightweightThemes.selectedThemeID

cor-el said

This means that not themes are installed and selected because otherwise selectedThemeID and usedThemes would have a not-blank value.

• lightweightThemes.selectedThemeID = <blank>
• lightweightThemes.usedThemes = []

This is strange. I have a total of 13 additional themes installed (beyond the "default", "light", and "dark"), including three that are animated. I currently have selected a theme called "Galaxy Green" that I downloaded from addons.mozilla.org (where I got all of my themes from). Yet I just checked my prefs and it is still showing these blank values. This is after my theme stayed put for the entire weekend.

I'm using this same theme on two separate machines (sync'ed) and they both show the same blank values. Could there be some kind of sync issue? Note, I found my prefs.json file in the same place mentioned by meowwl (in Weave), but it seems to be empty. The only thing in there is: {"ids":[]}

Maybe I should try removing and then re-installing the theme to see if the prefs are fixed.

I wanted to post a quick update: I unchecked "Add-ons" in the account sync options and the problem seems to have gone away. I've had "Green Galaxy" working on machine one and "Animated Matrix" working on machine two for well over a day now. Not ideal, since it doesn't allow me to keep my extensions in sync, but since I have most things set up how I like them, I can just re-check when I make changes to the extensions.

A further note: using a suggestion from another thread I also set the two preferences mentioned above to "false":

   lightweightThemes.selectedThemeID = false
   lightweightThemes.usedThemes = false

You can set the two Sync lightweight theme prefs to false to prevent the themes from getting synced.

• services.sync.prefs.sync.lightweightThemes.selectedThemeID = false
• services.sync.prefs.sync.lightweightThemes.usedThemes = false

That way you should be able to sync other add-ons.

The various services.sync.prefs.sync.* prefs set what prefs to include in syncing preferences.

Great option. I'll try it and report back. Thanks.

Unfortunately, setting those items to false did not seem to work. Both machine's themes disabled a short time later. So for now, I'm back to unchecking "Add-ons" in the sync options. That has continued to work for me.