Like others, this stopped working after the 94.0.1 update.

Fortunately the post by Carlos helped get it working again. His instructions that work are:

1. Disable the extension (NOT remove)
2. From Firefox Settings -> Language and Appearance -> Colors, uncheck the "Use system colors" and change the drop-down to "Always" in "override colors specified by the page".
3. Check a website that you've clicked links on to verify the color changed
4. Go back to the Firefox Color settings and change the drop-down to "Only with high contrast themes"
5. Re-enable the plugin

You should now see the clicked URL colors use the color you specified while the rest of the webpage uses whatever is determined by their style sheet.

Stopped working on Firefox 94. Carlos AM's fix worked for me - thank you!

No longer works. Used to love this, but no longer works with newer Firefox versions. :( Hopefully the developer will fix it.

Thank you! This extension is a life saver for those whose vision is not that great to see what web links you have already visited. This feature should be mandatory in all Internet Browsers.

Unfortunately, has stopped working on Firefox 94…
UPDATE:
Working again. First, I disabled the extension. Then, in Firefox's color settings, I unchecked "Use system colors" and selected "Always" in "override colors specified by the page". Used Firefox for a while, then went back to color settings, selected "Only with high contrast themes" in "override colors specified by the page" and, finally, re-enabled the extension.

Also stopped working, didn't found any other way to report

Been using this for several years has now stopped working on Firefox and Firefox nightly.

Been using this for over a year with no problems even when Firefox updates. Very grateful to the developer for this free add-on! Windows 10 21H1 on Dell Optiplex 5060.

Hello, I hope you are well? I love your addon, but for some time now it does not work. I always have to restart addon and then it works again.
Detailed error description:
I click on a link, the link colors in and then the link opens and I have visited the page.
Now I go back to the previous page and the link is not colored.
If I restart your addon in the addon settings it works again for a while. Do you know the problem, can it be solved? Thanks in advance for your effort.
Best regards,
Elena

I never needed an add-on before, in over 15 years, to get FF to use my chosen colour for visited links. But my PC died and I did not have a backup for my Firefox settings (stupidy stupid) and on the new laptop where I had to set up FF friom scratch, the link colour just would not work. This add-on has made my chosen visited link colour work again. Thank you very much.

🦊🦊🦊🦊🦊

It works for me (Firefox 82.0 @ Ubuntu). The only wish I'd have is to make it possible to enable/disable it on a per-site basis.

For the life of me I cannot get this add-on to work. On previous versions of Firefox there was one that worked well. I conduct a heck of a lot of research and one of these highlighters would be great if it worked and would save me a lot of time.

My Firefox for some reason stops to color visited link, I already made sure I am not in privacy mode, and 'Remember History' is turned on. And yes I tried to user other browsers, and they all worked, except for FireFox. I also did clean uninstall, then install fresh copy of FireFox, deleted profile folder to remove all preference, but nothing works. This addon is ONLY thing that color my visited link, because native Firefox on my Windows for some reason is broken. Thanks for making this addon!

Doesn't work at all. In Firefox preferences I set the visited link for red. Nothing. The links return to blue.
Firefox 78.1.0esr (64-bit)
2015 27" iMac

Modest functionality. More settings required: White list, black list, Individual settings for each site, Color selection.

Great add-on. I only wish it had a way to white-list specific websites. Hopefully future versions might have that.

The only one that worked for me. Awesome! Love it!

However, there is a problem. It works flawlessly on my desktop machine, but on my laptop, running the same Firefox 70 (64-bit) with the identical OS, it does not work. I removed and re-installed twice, to no avail. Please advise what I am missing. Thanks.

No configuration options whatsoever to be found, neither on the addons panel nor in any other icon.
The "default" color is some kind of dark purple, barely visible. Running FF 67.0.4.
Addon obviously deprecated, since it hasn´t been updated in more than 1.5 years.

Thank you. Now I can tell at a glance which Google search results I've already accessed and which I haven't. I research info across thousands (literally) of pages each year. The default colors between visited and not visited were near impossible to tell apart. Loading the same pages repeatedly while researching projects slows progress. Time saver you are :)

Could you please add button to toggle on/off ? cause some websites use the same or close background color.

This is great, this is great, this is great.

I love you dear developer.

I always had problem of remebering what links i opened/visited/read before.

Thank you very much.

Also had a question, in some websites i saw that this option in browsers may be used for extracting history by websites and privacy issues because of this reason.

Is this extracting my history by websites really applicable?

Although the convince of this addon unfortunately worth that privacy issues because the web really isn't usable for me without this :\


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Update/ reply to another comment: Addon works on Android

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Four Addons like this that are really great:

1. Visited link enabler (This Addon)
2. Gray visited links (use either this or that!)
3. Highlight bookmarks
4. Last visited Toolip