Does exactly what I need, but it is a pain to use it. Highlighting is extremely slow – it takes several seconds. The animation for color selection box is annoyingly long and also currently broken (it disappears).

This add-on made paper reading so easy for me!!

So far so good. I was looking for just the basic feature, but I found the multiple-word custom highlight feature even more useful!

I'd like word selection to activate the standard highlighting even when using custom colours (i.e. I select the word -> it highlights all instances with native colour + it shows the custom colours popup)

Custom highlights can be deactivated through the right-click menu. However I think it would be better to have a blank X button next to the other colours.

Merci au dev pour cette indispensable extension

Excellent Addon. Thank You.
One bug though. When the selected text has open and close brackets (...), the selection goes away, only the highlight remains. Pressing Ctrl-C after that copies no text.
Another problem- It does not work on simple text files. It also does not work on the mozilla addons site.
Thanks.

Edit- After few days of use I found it is full of bugs.

Didnt seem to work at all. Im on windows using firefox 65.0.2 (64-bit). I wanted to see highlighting in the scrollbar but did not.

This is an extremely useful tool, that helps increase my productivity in my day to day work. Will recommend to colleages as well.

Custom mode is quite slow, at least on my use case. So I am sticking with native mode, as it is significantly faster.

If only it was possible to click on the "number of occurrences" pop up to take you to the next occurrence, it would be perfect! :)

Excellent Add-on. Must have.
Very useful improvement — to have a shortcut to un-highlight all. Currently it's only page refresh.
Possible improvement — when multiple colours are set, every new selection gets automatically the next colour.

Very handy. The one thing I didn't like about Firefox's Find feature was that it doesn't show the occurrences on the side scrollbar like Chrome does, which makes it hard to actually find where the matches are. This addon provides that, and in my opinion this feature should be in Firefox itself.

Нужное и удобное дополнение разработали!

Sadly It does not work for a bigger pages.

Doesn't work.

Update:
Thanks to the develper, problems have been solved.
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1. It will always make my selected text be unselected when hovering around(custom highlighting & always enable).

2. There isn't a way to toggle the existing highlighting effect off unless I reload the page. I use custom highlighting mode with 3 colors. I notice there is an option"Keep text highlighted upon click in the page(when only one color is used)", so could it be possible to add one more option(I mean one feature) -- Toggle in-page highlighting effect by press a combination key?

simple and efficient!