Autocomplete pops up when next input is clicked

Question

NOTE This behaviour only occures in FireFox (as least in v66)

I have the following scenario:

• one input type text
• directly below one input type number
• due to pre submittions to the form, the text input provides auto complete values (e.g. Test1 and Test2)
• when I know activate the text input and click on arrow up of the number input, the auto complete values appear and causes the number input to increment the number to its max value

All this can be reproduced here: https://jsfiddle.net/ax7unjhb/2/ (FireFox only!)

Click text input to gain auto complete:

Click arrow up; auto complete appears again and overlaps number input:

Number increased to max value:

<form action="window.location.reload();">
  <input type="text" style="width: 100%;" />
  <input type="number" min="1" max="32" style="width: 100%;" />
  <button type="submit">
    Submit
  </button>
</form>

My question

What causes the auto complete to pop up, although I click another input? This is not the expected behaviour. When I click the increase button of the number input, I expect to increase the number by 1.