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When I added new themes the old themes disappear, why?

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I have had themes disappear when adding new themes. I counted the number of themes and counted (including the default one) 31 themes. Is 30 the maximum additional themes you can add? Can I increase this number? Are the deleted themes stored somewhere?

I have had themes disappear when adding new themes. I counted the number of themes and counted (including the default one) 31 themes. Is 30 the maximum additional themes you can add? Can I increase this number? Are the deleted themes stored somewhere?

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Firefox stores data of a maximum number of Personas (DEFAULT_MAX_USED_THEMES_COUNT=30)

If you install more Personas then Firefox will remove other Personas to make room for the new Persona, so it is best to keep a list or bookmark the site of your favorite Personas.

You can override this maximum by creating an Integer pref with the name lightweightThemes.maxUsedThemes and set its value accordingly.

The data of all installed Personas and its background color and text color are stored in the lightweightThemes.usedThemes pref in JSON object format ({"id":"#","name":"xxx",...}). The first entry of this pref is the currently selected Persona.


  • resource://gre/modules/LightweightThemeManager.jsm
const DEFAULT_MAX_USED_THEMES_COUNT = 30;

this.__defineGetter__("_maxUsedThemes", function maxUsedThemesGetter() {
  delete this._maxUsedThemes;
  try {
    this._maxUsedThemes = _prefs.getIntPref("maxUsedThemes");
  }
  catch (e) {
    this._maxUsedThemes = DEFAULT_MAX_USED_THEMES_COUNT;
  }
  return this._maxUsedThemes;
});