This certainly works, but unfortunately it appears to have a lot of performance issues. Even when not in use it can cause pages to stop responding.

It also doesn't provide any feedback when an invalid pattern is used etc.

Disappointing. Alternation with | doesn't work. Th extension's popup dialog hides half the page with useless controls when all I want is a functioning regex search.

The idea is good, a much needed extension after Mozilla killed all regex addons, but it doesn't work.
On my updated waterfox, (foo|bar) only worked once, but it only matched "foo"

The add-on doesn't fully work, and for as far as it does, is not very practical.
- I type in a regex and do 'search' but it doesn't always show the results it should. Oftenly it shows nothing in the result box, sometimes just one result where there are many more.
- The highlight function does find all matches. However, it would be nice if the page could jump to the first/next result, but that's probably what the search button is supposed to do.
- When using the highlight function without the 'global' flag, a result is that is not the first one may be highlighted, rather a random(?) one.
- It seems that this addon looks for matches in the html source code rather than the actual page. Therefore it also seems to match classnames, image paths etc. This is not great and the highlight function therefore has matches that can't be seen on the page!

It's a nice add-on, but could use some improvement!

This extension desperately needs use instructions. I haven't worked out how to get it to highlight text in a webpage that matches a regular expression, which is what I want, and what I thought the description said it would do.

There's no 'use RegEx' option when I type Ctrl+F, and when I click 'Preferences' on this extension, there are no options, and nothing that says what to type to make it work. I did eventually notice the 'Regex Search' button in the toolbar, but clicking that opened a confusing dialogue box, and when I typed a very simple JavaScript-style regex, it didn't seem to find anything on the page I'm on.

Perhaps I'm missing the point of this extension, but either it doesn't do what I want, or the UI is terrible. Sorry.

Couldn't wrap my head around how it works. The interface is confusing. I just want a way to CTRL + F a page and highlight results using regex. I couldn't figure out how to do it with this addon.

I too was hoping to see the search terms highlighted in the page. I just installed it so I know I have the latest version. Dev says it highlights on the page but I'm looking at the search it found and looking at the section of the page where I can see the term I searched for - it is not highlighted!

I have to copy the text in the result field then use Firefox's search (ctrl+f) to highlight the search terms found.

Limited usefulness as it currently stands but with Firefox 57, this appears to be the best out there.

UPDATE: I visited the github link you posted in your reply but only saw the XPI file for Windows - will this also work on Linux? (I wonder why there isn't an option to reply to a developer response!)