This is the first extension I am reviewing without having tried it. I don't need to try it because colored tabs are not something I need.
This is a review of the extension page and the bad description posted by the author. Out of two paragraphs, there is almost nothing about how this addon works. The 1st paragraph is just generic nonsense and false praise about how this is the most important extension I'll ever need, and the first one I need to install. That is NOT a description, that is BS.
The second paragraph is a review quote from a user who loves this extension, for whatever reason.

Horrible presentation, no description to speak of, all BS and lies, nothing that explains what makes this extension SOOO good. This type of a front page is just very unappealing, and I'd never want to try any extension with that info.

Fail!

I should have made proposals on the site if I had found how to create an account.
This extension is a good idea (and replaces things that no more run), but needs to be improved.
By the way it appears that critics for two different extensions appear on the same page here.
I tested the one with Web Extension, as I use Firefox Quantum, version 59.0.2 - I presume this extension is somewhat recent.
About the results, I see the active tab displayed with a different colour, and this is why I installed the extension.
That being said, this background colour is at random, and the foreground colour (font colour) is fixed (in the options) so this not always optimum.
I regret not being able to choose colours for other tabs, classically a set of colours for not loaded tabs, another for inactive tabs ...
Tab Mix Plus has accustomed us to use a nice user interface to choose the colours, well let us forget that for the moment being, it takes some time to develop.
What would really be useful is that the extension sets a style name for the active tab, one for the tabs that are no more loaded, one for the other ones. And also that the documentation gives those style names.
With that, we could personalize properly those styles in userChrome.css (at least the advanced users could do that).
In a second time, as an options interface is proposed, it would be nice that for each of these styles it allows to give a foreground colour, and a background colour. Some of them miss. If time allows, some other attributes as bold could be smart too.
When this urgent stuff is done, I should like to mention that after installing the extension I had to style my personal bar (placestoolbar), as the extension modifies its background colour, and the font colour it had was no more adapted.
If you have time to do some tests at this level, it will help, too.
Thanks for the good job.

Useless garbage that will make you feel like a fruitcake.

The new Colorful Tabs doesn't work with Quantum. Quantum is crap any way ! ! ! !

Does not work with Quantum

Bad colors. Not like in Vivaldi. Youtube isn't red, for example.

IT DOES NOT WORK

It does not work in Quantum. It overwrites my Personas theme with an aweful, random colour and does nothing for tabs. Useless, unfortunately. This was my favourite add-on prior to Quantum but is now nothing. Such a shame.

Quantum is horrible. It's like they deleted the fun stuff and and replaced it with... nothing. Even the bookmarks are inconvenient to use. I've been using Edge on my new laptop. It's better than this mess.

people still don't want to understand that at the time it's IMPOSSIBLE to color all the tabs through an extension as it used to be before quantum. maybe it never will.

blame mozilla for this... personally i'm sticking to 52.x ESR, stuff this quantum crap.

I like using "ColorfulTabs because each tab that's open has a different color. You can change the color of any tabs,
that are open, to a color you prefer. And if you have tabs for the same site, different pages, it will show a fading of different colors that the first page of that site has.

A once great extension, like MANY others, laid to waste by Mozilla with their lame implementation of the incomplete Quantum with most APIs unavailable to addon devs.

Aspect agréable; facile à mettre en place

Doesn't work as shown in the extension page screen shot. Only the selected tab is colored randomly. The bookmarks and address bar rows are also colored with the same random color.

Still not working properly.

Not working at all properly in Quantum Firefox 58. It was GREAT in pre Quantum Firefox. I loved how it gave different colors to different tabs, because with this simple feature, I could much more easily see, & manage, working with lots of multiple open tabs.

In Quantum 58, it doesn't work that way at all. It just creates a weird color spread collage, which all tabs get uniformly. It sits there, and does that & nothing else. The homepage to alter settings is confusing, and doesn't seem to help at all. In the old preQuantum version, it would simply give a different pleasant color to each tab top header, so it was easy to find different tabs, and organize them. This version is totally different, and careless and distracting, unsettling, and dreary. I've disabled this, because it is nothing like the old ColorfulTabs in preQuantum Firefox. If it gets fixed, and works like it used to, I'll be happy to enable it & use it all the time. But this version, no, it creates more visual clutter, rather than organizing my tabs properly, so it does the OPPOSITE of what I'm looking for.

I want to remove this from Firefox & can't find where to do it.

Tabs were colored last year. Do that again please.

Colorfull tabs latest update wipes out any attempt to use a theme. If you like a plain white theme i guess that's not too bad. Very disappointing to me though as I like color in my themes. I've used ColorFull Tabs for DECADES without a problem. Until now. A real shame I've had to delete it. I liked it when it worked.

Ich liebe ColorfulTabs wegen den schönen Farben und weil man damit die einzelnen Tabs gut unterscheiden kann.
E.S.

Ne fonctionne plus avec Firefox 58 Dommage

The Colorfultabs is terrible. I does NOT work like the old Colorfultabs. It colors the whole top of the page instead of just the tabs. Also they just change the color of everything with every other tab. I am so disappointed. I never asked for Firefox Quantum. My first impression? I HATE IT!