Hello, Wim. Couldn't find a bug report page, so I'm posting it here.
There's a bug with Regex's Lookahead/Lookbehind where it mixes up colors of the highlighted words if a pattern containing Lookahead/Lookbehind was found (at least that's how I think it works).
To reproduce this you need to create three lists and color them red, green and blue. Then add to each list one of these patterns: "r(?=[a-z])", g(?=[a-z]), b(?=[a-z]). Then reload a page and see that a lot of the highlighted letters don't match their colors. It will also mix up the colors of patterns not containing Lookahead/Lookbehind if you add those as well.
A couple of requests: could you please make the list of word lists slimmer? I usually make a bunch of differently color-coded lists for websites, and sometimes it requires some amount of scrolling to get to the list I need. Also, notifications that the list is limited to certain websites are unnecessary because, you know, every list should have those. Also, case-insensitive sorting method for lists and words would be appreciated.
Other than that, it's a "Must Have" add-on, greatly improved my browsing experience!

Great tool!

This app is ok. Doesn't always pick out all the correct words to highlight.

Really useful addon! Use it on nearly all my brwosers, works flawlessly even on something like Edge!

I lost all my lists after import some lists from another pc. Please consider to develop a auto-backup or multi-list combining feature. Many thanks.

Long ago this was a very stable and excellent program . . . not so much anymore. I have tried running this on Chrome, Firefox and Edge and the same thing happens on each browser . . . it simply stops working. I mostly use it on titantv.com to highlight favorite programs. It's just not stable anymore. It will hold the words for a little while and then suddenly they're all gone again. This is too bad, because it "was" a great program. Anyone know of a similar program?

но после обновлений Mozilla Firefox похоже бывает что вылетает. Переустановка помогает

Awesome idea. But I'm experiencing an errors:
1. Some sites start to partially duplicate text blocks if it has highlighted words. Need to refresh the page to fix it (YouTube), but sometimes even refresh doesn't solve the problem (Facebook).
2. Almost all highlighted words have a vertical strip to their right and are underlined for some reason.
Win10, Firefox 83.0

Seems like a good app. Except new lists aren't appearing on the dropdown menu. Only the Default Group. Not sure why but I can live with it for now. Otherwise, it's great.

Firefox 81.0.1 (64-bit)
Version 5.2

Why are all Non synchronized list remove and settings restore to default after clearing firefox Offline Website Data?

It was great addon (and it still is) up to v4.9 for my Firefox 56.0.2. After that release all next releases are crap - they are completely not working in the same Firefox 56.0.2. After updating of this addon all my lists of words are gone. I click on + to add a words - and nothing happens. Clicking on other buttons doesn't work too. Addon completely dead and mulfunctional.

I enjoyed this addon until the recent update. First of all, this is a great addon to have and did a great job highlighting the keywords. I have over 100 words through various sites to make my tasks easier.

Now to the point of why I am not satisfied with the update. All of my keywords that I set up through this addons are gone, it just poofed. It happened right after the update, I believe, was a major revision of the addon. Now, I don't remember every words and it affect my productivity greatly and made a negative impact on my workflow due to recent update. I depends heavily on HighlightThis as it is part of my productivity.

Frankly, I am disappointed with this. I am expecting a quick export of my list before pushing the update. And now it is gone, I have no way of recovering those keywords that took me a while to get it in the list.

Unfortunately, I will be uninstalling this addon. It take too much work for me to put the list back. What is worse is that my memory is not that great, that means I can't even remember the key words that I set it up in the addon including the websites.

After 5.1.2, I can't see any highlighted results in editable fields (test boxes), but the found number is only shown on an icon of menu bar. I hope to check and correct it immediately. Or could you tell me how to install older version ? Because I need this addon for work.

(added at Aug.06, 2020)
Thank you for your quick revised action! But some type of text boxes are not highlighted yet. In older versions, those boxes were highlighted.