User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:66.0) Gecko/20100101 Firefox/66.0
Steps to reproduce:
From a blank profile, add a bookmark where the URL uses an IP address rather than hostname, e.g. https://10.1.2.3/foo
Begin typing in the Address Bar, e.g.:
Autocomplete fills begins to fill in the hostname, i.e. https://10.1.2.3 with the untyped portion (".1.2.3") being selected (normal behaviour so far).
Type the next character (.) and the incorrrect behaviour occurs.
Upon typing the ".", the autocompleted URL changes to https://10.0.0.0 and the untyped "0.0.0" part is NOT selected with the cursor still placed between the "." and the "0.0.0". As the user continues to type, the "0.0.0" remains appended to the end of the URL, e.g.:
This behaviour seems to occur for any IP-based bookmark; as soon as the first "." is typed, autocomplete appends "0.0.0".
It is unclear why autocomplete is appending "0.0.0" in the first place, but in any case the normal behaviour in the Address Bar is for the autocompleted (untyped) part of the URL to remain selected; this does not happen in this case.
This problem was not observed prior to r66.