The Find bar has settings to search for "Whole Words" and "Match Case" that are hidden when you use Quick search, so open the Find bar via Ctrl+F and check these.

Thank you cor-el, Yes, It's a good solution for this case. Actually, it helps me, and I had completely not aware of about that options in spite of that I had uploaded 2 pics haha...But I am yet considering that this issue might be more a bit little complicated. Please let me write about it here more a little, but I have been partially coming back to Firefox recently since I had switched to chrome many years ago so I'm a beginner of Firefox and search. Now I generally understand its behavior like below :

• "Whole Words" means completely matching word or sentence selected as each character excluding overs-and-shorts.
• "Match Case" distinguishes Uppercase and lowercase ( means case sensitivity from in the result of "Whole Words".).

Certainly, phrase searching highlights all phrases in the same as my search phrase if I switch off "Whole Words". Now I have learned it simply. But that My case is an issue that Firefox distinguishes the search phrase by whether the HTML element including the phrase includes extra half or whole-width space or not. It seems like that isn't a matter of whether Uppercase, lowercase or completely matching. It seems like this is the matter of whether there is a half or whole -width space or not.

In fact, Firefox highlights only the phrase which is not completely matched in Case-A & B that in the pictures attached to a former post. The Case-A especially indicates a weird conclusion to feature of "Whole words" in spite of that search phrase match completely.

I now saw the page below: Search for whole words only

I wonder if I couldn't understand the meaning of "whole Words". As another example, searching the word "comma."(comma plus dot) with "Whole Words" performs hit less than all that words in the page. Essential of the result is as well as Case-A. The key point always is whether there is a half-width space or not.

If there is a half-width space next to the word "comma."(comma + dot), Firefox can highlight all that "comma." even using "Whole Words" feature, but when it deletes the half-width space from the word "comma.", Firefox cannot highlight it anymore.

"Whole Words" is working correctly right? if so, this feature is difficult for me a little.

Thank you.

EDIT: completely resolved. I could understand the behavior of "Whole Words". This issue occurs due to almost misunderstand of "Whole Words" at the user end. It's me this time.