KeeBird seems to break Thunderbird Quick Filters

[sandromario]

Thunderbird version: 68.5.0 (64-bit) Keebird version: 2.0.0/2.0.1

Keebird seems to cause a strange behaviour of Thunderbird Quick Filters.

Steps to reproduce:

1. Make sure Thunderbird uses tabs.
2. Type letters into the Thunderbird Quick Filters textbox, until Thunderbird says that no emails can be found.
3. Now quickly type two letters in a row (e.g. hit the same key twice with no break in between).
4. Thunderbird now opens a new tab for the search. This is unexpected behaviour. A new tab should only be opened when Enter is pressed.

This behaviour does not occur with KeeBird disabled.