Did you create the lowercase URL yourself and do both URLs work (no redirects) ?

On most servers (at least on Linux) file paths are case sensitive, so you need to create/update the URL to the final URL you get in the location bar especially in case of a server redirect. You only get the blue highlighted star when the bookmark URL and the URL in the location bar exactly matches. Otherwise you need to update the URL in the bookmark or create a new bookmark with the correct URL.

thanks for your answer.

But, for twitter if the user change twitter account name "abcde" to "AbCde". it's not work.

i've lots of urls in my bookmark. so it's pointless try to update urls everytime.

why did not firefox recognize urls which are the same but different upper-lower case?

i gave an twitter example. please try.

if you click first link and go to twitter account page than click any tweet and than click account home page again, it's change to upper case url.

so firefox cannot recognize. star is not turn blue but urls are same and it is in my bookmark.