Mrfuyu

There's no need of this feature in my opinion. Just define under "Symbol" a user defined icon and leave this entry empty -> No icon in addition to the indicator...

@Zranz hm sorry, it works for me :/ I use FireTray v0.6.1 with v45.2.0 Thunderbird on 16.04 Xubuntu

I just tested it with an 1x1px transparent png and it also worked on Xubuntu. Maybe you could try this ;). I attached the used image. Download: [https://cloud.githubusercontent.com/assets/14253537/17790634/a80d538a-6597-11e6-8cc8-57b522958d8a.png] 

Ok, that's really strange :/ What you also could try is to change the default icon under ~/.thunderbird/xxxxxx.default/extensions/firetray-id/chrome/skin/icons/linux/hicolor/22x22/apps/thunderbird.png (not sure but i think this is the default icon that is...