As per $summary, this is under Linux with KDE4 and generic X11 frontend
Probably a regression as it works to some extent in 5.3
Steps to Reproduce:
1. Start Writer, Impress, Draw or Calc
2. Ctrl-F to make find toolbar appear
3. Undock the find toolbar (drag it by grip out of its docking area, with LMB pressed)
4a. Type some search expression into the text field therein
4b. Click 'Match case' checkbox and press Tab key to move focus to the next active control
4a and 4b doesn't work, neither can one type nor move keyboard focus with Tab. This makes undocked toolbars completely non-accessible
It should work, this is bad for a11y
User Profile Reset: No
User-Agent: Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:58.0) Gecko/20100101 Firefox/58.0
Ouch, After rereading the steps, I've just realized it's the same as in bug 116563.
I thought you were reporting another issue...
*** This bug has been marked as a duplicate of bug 116563 ***