This issue affects Firefox 51, but not Firefox 49 (my guess is it also affects 50, but I have not tested (I presume this bug is related to the introduction of the "whole words" button)). if clicking "match case" changes the result so that there are zero matches where there were previously some matches, or so that there are some matches where there were previously zero matches, the highlighting does not get updated. A) reproduction steps (highlighting remains when it shouldn't): 1) go to https://www.mozilla.org/en-US/firefox/51.0a2/auroranotes/ 2) press Ctrl-F (or whatever bring up the find toolbar on your system). 3) ensure that "highlight all" is selected 4) ensure that "match case" and "whole words" are NOT selected 5) type "PASSWORDS" (in caps) into the input 6) press "match case" result: lower-case "passwords" instances are still highlighted expected result: lower-case "passwords" instances should no longer be highlighted. B) reproduction steps (highlighting doesn't occur when it should): 1) go to https://www.mozilla.org/en-US/firefox/51.0a2/auroranotes/ 2) press Ctrl-F (or whatever bring up the find toolbar on your system). 3) ensure that "match case" is selected 4) ensure that "highlight matches" and "whole words" are NOT selected 5) type "FORM" (in caps) into the input 6) unselect "match case" result: lower-case "form" instances remain not highlighted expected result: lower-case "form" instances should become highlighted. ***Please note that this bug outlines one specific issue that seems to have been introduced with the addition of the "whole words" button -- there are actually more issues (different combinations of these controls done in different orders produce incorrect highlighting and/or incorrect summary of matches and/or incorrect red background for the input), but I don't think it's probably necessary to document them all right now, as whoever works on this will presumably be looking to ensure all combinations work correctly.

I can't reproduce the issue with the latest FF51, the find toolbar text field becomes red and 0 instance of the search is found. Could you check you're running the latest build of FF51?

I just re-tested with 51a2 (2016-11-05) and can still reproduce. perhaps the results aren't always consistently reproducable. I'm seeing other bugs I alluded to which present sometimes and not others. see if you can reproduce this one?: 1) go to https://www.mozilla.org/en-US/firefox/51.0a2/auroranotes/ 2) open find toolbar, ensure none of options are depressed 3) type "passwords" 4) select "highlight all" (at this point 2 instances should be highlighted) 5) in the input field, select all, and then press backspace when i perform the above steps, the highlighting remains, even though it shouldn't i'm using the Linux 64-bit build from mozilla

alternatively, when following the reproduction steps above, if you backspace one character at a time, the highlight will be updated until you backspace over the last character

I can reproduce your 2nd testcase in comment #2 with FF51, but not 52 (or 50). So it's probably already fixed somehow. Mike, do you know if this issue will stay in FF51 when this build will migrate into the Beta channel?

Aie, I need to uplift bug 1301941 anyway to have this fixed in 51! My apologies and thanks for filing this bug!

Mark 51 fixed as bug 1301941 was fixed in 51.

As per comment 16 from bug 1301941, setting status-firefox51 to verified.