STR (as recording video part I):

1. install any CJK IME and Firefox 83.0
2. toggle awesome search mode with the IME
3. type any word as search terms

Autall:
search mode is quit before the search term can be selected

note:
when adding a space before the search term, search mode won't quit (see recording video part II)

I can reproduce the issue on Nightly84.0a1 Windows10.

STR

1. Focus Address bar
2. IME ON
3. Type amazon and choose a candidate string "amazon", then commit
4. Select "Search with Amazon.com" from dropdown
   --- [Amazon.com] is indicated in the Address bar as expected
5. Type any word
   --- BUG!. Search mode is quit. [Amazon.com] will disappear.
6. Hit Enter
   --- BUG!. Search the word with Google :(

just some more details:
this bug can NOT be reproduced if:
a. you use @searchengine keyword
b. you click the engine manually

Also happened on Microsoft New Phonetic(bopomofo).
System: windows 20H2
Firefox: 83.0

Is it possible that a patch is introduced within train of 83?
This is a bit annoying bug though very old users might click the engine buttons so override this.

(In reply to lolipopplus from comment #4)

Is it possible that a patch is introduced within train of 83?

Sorry, I am not a developer.

[Tracking Requested - why for this release]: Search from addressbar is broken

No priority and severity ?

Well, afaict this is not actually a regression, it just didn't work from the beginning of tab-to-search implementation.
and there are workarounds, as stated in comment 2.
Search is broken if tab to search is used, but not in the other cases, right?

I posted some Try builds in https://bugzilla.mozilla.org/show_bug.cgi?id=1673669#c19, testing is welcome

Should have been fixed by Bug 1673669.