Affected versions

• Fx 78.0b7
• Fx 68.9.0esr
• Fx 76.0

Affected platforms

• Windows 10 x64
• macOS 10.15
• Ubuntu 16.04 x86

Steps to reproduce

1. Open about:preferences
2. On Search text field enter "search" .
3. On Language section click on "English (United States)" button that brings up a dropdown menu.
4. Click on "Search for more languages...", the last item from dropdown.
5. Close the "Firefox Language Settings" page.
6. Click again on dropdown.

Expected result

• The searched word is correctly highlighted in dropdown (see. Before.png)

Actual result

• The searched word is no longer highlighted in dropdown (see. AfterClickAgainOnDropdown.png)

Regression range

• I will come back with regression range ASAP.

Notes

• In Fx 72.0.2, Fx 73.0, Fx 75.0 the searched word is not selected even at the first click on dropdown.
• There are differences between Firefox Nightly ui and Firefox Beta ui, regarding Language section from about:preferences.

This is specific to the Browser Languages dropdown, because that list is rebuilt after the dialog is closed since the supported languages may have changed.

There are two issues at hand:
1, the menuitems are not created with the 'highlightable' attribute.
2, the highlight range is not re-applied in the new nodes

The code at issue is https://searchfox.org/mozilla-central/rev/1304678d837c17811617754fd446794b774afe94/browser/components/preferences/main.js#1013-1031

To test this on Nightly builds, you will need to set the following prefs:
intl.multilingual.downloadEnabled = true
intl.multilingual.enabled = true

The severity here is really low, since the findInPage feature is here to help users find what they're looking for among the many screens within preferences. If the user has found the language dropdown then highlighting the results after they have already interacted with it provides very little value.

Restoring the attribute here is simple, but restoring the highlight range and applying new highlight ranges in the case of new matches is more difficult and provides little value. Thanks for filing the bug, it is good to know that this bug is not widespread.

Some search results are not highlighted in about:preferences/"Cookies and Site Data" section. For example search for "firefox", scroll through the Search Results page and see if every time the searched word appears and it's correctly highlighted, "Clear Data" button not have the highlighted tooltip, but the "Clear Data" window contains the "firefox" word. Tested this on Fx 85.0b4 using macOS 10.15 and Win 8.1 x64 platforms.

It's been a while since this bug was filed, and it may be obvious as such, but I want to be clear here that fixing this bug is low on our priority list and is unlikely to get attention anytime soon.