Icon changes after count is cleared

[m-schmitt]

I'm glad to stumble upon this new Tab Badge add-on. The same-named add-on I used before stopped working with Firefox Quantum.

I'm using Tab Badge with Fastmail.com. What I see is this:

1. Favicon starts out as a square envelope.
2. Unread mail arrives. Badge is added to the square envelope.
3. When all of the mail is read, the badge is removed but...
4. Now the favicon is different than in Icon changes after count is cleared #1; it is an envelope in a circle.
5. If refresh the page then I'm back to favicon Icon changes after count is cleared #1.

What I'm suspecting is that the icon in #4 is what's in the web page but a script is changing it to icon #1.

In step #4 above what appears to happen is the favicon first just drops the badge (i.e. it is icon #1) but then it quickly changes to icon #4. Note that this only happens with Tab Badge enabled.

(Note that there are really three favicons: the square envelope (#1), the envelope in a circle (#4), and a different envelope in a circle favicon (let's call this #5). When refresh the page it first sets it to #5 but then quickly changes it to #4.)

I don't know if you can recreate this without a Fastmail account. Let me know if there's anything I can do in the inspector.