Removed custom folder icon reappears after relaunch

[ScriptHippie]

Quickfolders 6.15pre173 (but also in previous pre-versions)
Thunderbird 147.0.2 on macOS Sequoia

Removing a customized folder icon works via both the folder command menu and the toolbar button.
After relaunching TB though, the icon reappears every time.

Looks like a regression of issue #546

[ScriptHippie]

The removed customized icon also shows up again in any additionally opened window during the same TB session.

[ScriptHippie]

As I re-read #546's last comments, I can confirm that the issue only exists for the last custom icon that exists. With that in mind, one can work around by setting some odd/rarely used folder to use an icon as a "sacrifice" folder :) or manually edit the .json file as described in the other issue.

[RealRaven2000]

As I re-read #546's last comments, I can confirm that the issue only exists for the last custom icon that exists. With that in mind, one can work around by setting some odd/rarely used folder to use an icon as a "sacrifice" folder :) or manually edit the .json file as described in the other issue.

this is most peculiar. the "returning phantom icon" is most likely stored by Thunderbird itself in the folder properties (I am not actually sure where this is stored physically or at what point Thunderbird persists these. one theory would be if you removed the local version of the folder and then redownloaded it via IMAP it might lose it's icon as well).

So the tricky bit here is the removal of the property (and persisting that decision), not just deleting it from a JSON file that QuickFolders governs. But I need to make a proper test case and see if I can reproduce the issue here maybe I can find the gap in code.

Here is the crucial bit in my function QuickFolders.FolderTree.setFolderTreeIcon() :

  setFolderTreeIcon: function (folder, iconURI, silent = false, styleSheet = null) {
....more code...

      try {
        if (!iconURI) {
          // when do we force this to be executed?
          util.logDebug(
            `FolderTree.setFolderTreeIcon(${folder.prettyName || folder.localizedName}, empty)`
          );
          util.logDebugOptional(
            "folderTree.icons",
            `REMOVING:\n${selector} {\nbackground-image\n}`
          );
          QuickFolders.Styles.removeElementStyle(ss, selector, "background-image");
          folder.setStringProperty("folderIcon", "noIcon");
          folder.setStringProperty("iconURL", "");
          folder.setForcePropertyEmpty("folderIcon", false); // remove property
          return;
        }
        // 

one complicating fact is that the built in function getStringProperty sometimes throws an exception on folders in Thunderbird, I have no idea why.

[RealRaven2000]

... Reading the code in setFolderTreeIcon() a bit further, we also see there may be multiple folder trees (due to Thunderbird having separate documents for its tabs). So it might be helpful to set up a test where multiple Thunderbird tabs are open which show different folders and maybe at least one tab with a single message opened - just because no tree is shown here it may still be acting like a 3pane tab and may have the element simply collapsed. Not sure about that last one, but Thunderbird is a complicated beast.

    // need to do this for ALL 3pane tabs!
    // let doc = || this.document document; // 3pane doc
    // need to iterate this.documents!
    for (let docInfo of this.documents) {
      // make sure this tab still exists
      // make sure this tab still exists
      let doc = docInfo.document;
      // check if tab is illegal (was closed in the meantim)
      if (!docInfo.tabOrWindow.chromeBrowser) {
        continue;
      }

      try {
        if (!iconURI) {
          // when do we force this to be executed?
          util.logDebug(
            `FolderTree.setFolderTreeIcon(${folder.prettyName || folder.localizedName}, empty)`
          );
          util.logDebugOptional(
            "folderTree.icons",
            `REMOVING:\n${selector} {\nbackground-image\n}`
          );
          QuickFolders.Styles.removeElementStyle(ss, selector, "background-image");
          folder.setStringProperty("folderIcon", "noIcon");
          folder.setStringProperty("iconURL", "");
          folder.setForcePropertyEmpty("folderIcon", false); // remove property
          return;
        }

[RealRaven2000]

You can get additional debug detail in js console by setting

extensions.quickfolders.debug.folderTree.icons = true

via Advanced >> Debug Mode >> Settings:

[RealRaven2000]

I think I can fix this.
Testing it, first I found an exception was thrown in Thunderbird beta 148.0b6:

setFolderTreeIcon
folder.setForcePropertyEmpty is not a function
 aSourceName: chrome://quickfolders/content/quickfolders-folderTree.js, line: 562, copl: 0, flg: 1 setFolderTreeIcon
  chrome://quickfolders/content/quickfolders-folderTree.js:562:18
onRemoveIcon@chrome://quickfolders/content/quickfolders-interface.js:3399:34
removeIcon@jar:file:///I:/Thunderbird_Profiles/ct4akusa.Beta-Test/extensions/quickfolders@curious.be.xpi!/chrome/content/scripts/qf-messenger.js:744:35
....

so I am trying to avoid it by guarding against it being removed / missing, so that the following code can be executed.

          if (typeof folder.setForcePropertyEmpty === "function") {
            folder.setForcePropertyEmpty("folderIcon", false); // remove property
          }

Apart from that I found the core of the problem that setFolderTreeIcon() returns without a value, it should return true, this wayu the calling function onRemoveIcon() detects that something was changed and forces storing a new version of quickFolders-FolderTree.json in the extensions folder. note the usage of the isChanged flag:

	if (folders) {
		for (let i=0; i<folders.length; i++) {
      let folder = folders[i];
			if (QuickFolders.FolderTree.setFolderTreeIcon(folder, null)) {
				isChanged = true;
			}

			entry = model.getFolderEntry(folder.URI);
			if (entry) {
				// if button visible, update it!
			  folderButton = this.shouldDisplayFolder(entry) ? this.getButtonByFolder(folder) : null;
				model.setTabIcon (folderButton, entry, ""); // will only modify stored entry, if tab not visible.
			}
		}
		if (isChanged) {
			QuickFolders.FolderTree.storeTreeIcons();
		}

[RealRaven2000]

So writing the removal code wasn't all that hard (just returning true to tell the calling function to save a new version of the json file) - but restoring the correct folder icon to "fill the hole" turned out extremely difficult. for now I am just hardcoding a very specific rule in my own style sheets that uses the super specific rule targetting this particular img.icon:

#folderTree li[id$="…"] > .container > .icon {
  content: var(--icon-folder);
}

that is currently defined here in Thunderbird's mail/icons.css :

--icon-folder: url("chrome://messenger/skin/icons/new/compact/folder.svg");

slight disadvantage this icon is also used for special folder such as inbox, drafts etc. but it;s better than leaving a hole. this is only temporary until Thunderbird is restarted and the obscure native rules paint all correct folder icons. Test version here:

QuickFolders-mx-6.15pre216.zip

Edit: slightly improved with a correct value avopiding double url(url()) encoding (improved CSS above):
QuickFolders-mx-6.15pre217.zip

---

To install version above download zip file and drag the file into Thunderbird Add-ons Manager (do not extract contents, it won't install like that).

[RealRaven2000]

@ScriptHippie : did you test pre217 by any chance?

[ScriptHippie]

Thanks much for getting into this issue so deeply. I just tested with pre217 (TB 148.0) and, unfortunately, the issue behaves exactly like before (= last custom icon remains). Thus, I did not observe a "hole" icon left behind either.

Attaching a log file here under debug mode, but it seems the "remove" command did not reveal any extra information (line 40).
I tested between a Gmail IMAP account, a regular IMAP account, and a local folder, and found no difference.

One tidbit may be worth mentioning: For one of my test folders, I set a custom color. That custom color is always immediately shown as set before, once a customized icon has been removed. So TB remembers that color setting regardless of custom icons being placed "on top"; which is interesting, I would have expected TB to show the generic default afterwards. Well, I do not know how this is all represented internally in the data layer.

console-export-2026-3-5_13-1-2.log

[PascalNetenvie]

Hello,
On my side i have my custom icon displayed,

with classic tb folder icon (wireframe) displayed on top ^^

[RealRaven2000]

Thanks much for getting into this issue so deeply. I just tested with pre217 (TB 148.0) and, unfortunately, the issue behaves exactly like before (= last custom icon remains). Thus, I did not observe a "hole" icon left behind either.

Attaching a log file here under debug mode, but it seems the "remove" command did not reveal any extra information (line 40). I tested between a Gmail IMAP account, a regular IMAP account, and a local folder, and found no difference.

I can't reproduce this right now with Thunderbrid 150.0a1 (latest alpha version)

are you sure you enabled Debug mode and
extensions.quickfolders.debug.folderTree.icons = true?

I am missing messages that prefixed with "QuickFolders {FOLDERTREE.ICONS}" like this:

QuickFolders {FOLDERTREE.ICONS} 17:40:15.730  [0 ms]  
REMOVING:
#folderTree li[id$="aW1hcDovL3RodW5kZXJiaXJkZGFpbHk2NyU0MGdtYWlsLmNvbUBpbWFwLmdtYWlsLmNvbS9BZGRvbnMvRmlsdGFRdWlsbGE="] > .container > .icon {
background-image
}

console-export-2026-3-5_13-1-2.log

[ScriptHippie]

are you sure you enabled Debug mode and
extensions.quickfolders.debug.folderTree.icons = true?

I am missing messages that prefixed with "QuickFolders {FOLDERTREE.ICONS}" like this:

debug.folderTree.icons was FALSE. Find attached another log file excerpt below, with the setting on TRUE. The first mention of FOLDERTREE.ICONS is at line 198. This is the moment I used the remove command on that last custom icon.

console-export-2026-3-9_20-14-57.log