System: Win10 (Home as well as Pro), TB 68.2.2 (32bit as well as 64 bit), Mail Redirect 0.10.6
Behaviour: Mail Redirect functionally works fine, but it affects the "Customize" feature of the tool button lists. Whe MR is activated, tool buttons from any(!) extensions neither appear in the "Customize toolbar" dialog, nor in the totolbars they had been attached to previously. When deactivating MR. all works fine again.
Error Console:
Error initializing file output stream C:\Program Files\Mozilla Thunderbird\chrome\icons\default\msgMailRedirectWindow.ico: [Exception... "Component returned failure code: 0x80520015 (NS_ERROR_FILE_ACCESS_DENIED) [nsIFileOutputStream.init]" nsresult: "0x80520015 (NS_ERROR_FILE_ACCESS_DENIED)" location: "JS frame :: chrome://mailredirect/content/mailredirect-prefs.js :: unpackIcon :: line 334" data: no] mailredirect-prefs.js:343
unpackIcon chrome://mailredirect/content/mailredirect-prefs.js:343
<anonym> chrome://mailredirect/content/mailredirect.js:440
<anonym> chrome://mailredirect/content/mailredirect.js:446
loadScript resource:///modules/Overlays.jsm:566
load resource:///modules/Overlays.jsm:231
load resource:///modules/Overlays.jsm:48
observe chrome://messenger/content/parent/ext-legacy.js:229</anonym></anonym>
This error message somehow makes sense, for the designated output directory is read-only in Windows 10 for standard users and needs admin privileges for writing.
The error message is unrelated to the toolbar customization issue. It is because Mail Redirect tries to place a custom icon fot the redirect window in the program folder. Without this icon, the redirect window has the same icon as the normal Thunderbird icon, instead of it's own icon. This is because starting in TB60 the icon isn't read from the extension directory anymore.
Can you specify which toolbar icons aren't shown anymore? Is it from the main Mail Toolbar or from the message toolbar? And which icons aren't shown? Mail Redirect's icon itself or only icons of other extensions? And are the icons not shown in the toolbar itself, or are they not shown in the customization sheet or window? Can you give me an example of such an extension?
And last but not least: which way of customizing toolbars do you use, sheet of window, e.g. what's the setting of the pref toolbar.customization.usesheet?
toolbar.customization.usesheet is set to false - but:
I checked behaviour again, also playing around with other extensions, and have to admit: there seems to be a general issue with Thunderbird's main toolbar, not explicitly with Mail Redirect.
So I interpreted the error mesage in a wrong way, and fixing it will not solve my toolbar issues.
But be aware that your attempt to copy the icon to the installation directy will not work in Windows 10, for you need admin rights to write data in sub folders of the "Programs" directory.