User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:66.0) Gecko/20100101 Firefox/66.0
Steps to reproduce:
Started a global search query and then as soon as thunderbird shows suggestions (e-mail addresses that match the string I have typed into), navigate down to one suggestion (a matching e-mail address
Instead of searching for messages related to the selected mail address (firstname.lastname@example.org), Thunderbird reproducibly only searches for the string I have typed into the search field. This behaviour occurs only when I use the keyboard to navigate down to the suggestion, not when I use the mouse. However, since I use the keyboard to type in the search string, the natural work flow is that next I use the keyboard to go to the suggestion that I want to select.
Just the same as when using the mouse to select a suggestion: Thunderbird should perform a global search over it.