Almost perfect, but it's missing the ability to set custom referrers for different websites.

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Hello. At the screenshot in the title of the window a wonderful font is used. Dude, is it convenient for you to read the text in this font?
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Your add-on is very useful. I use it and I am very pleased.
Man, I just confused the assessment. I put you 5 stars, and your add-on is really good.
And the font on the screenshot made me laugh heartily.
Read this my comment, and then I will delete my first comment about the font.

Thanks. Good luck.

Well scripted, but sadly, this addons connects firefox at 151.101.120.133 at startup. Not trustful.

Great. Far superior to other referrer blockers I've used. Just for starters, intelligently allows within-domain referrers to be passed, which makes sense since you generally trust that domain. Other referrer-blockers' failure to do that causes the great-majority of problems.

Sehr gut für mehr Privatsphäre!
Hier wird alles hervorragend und leicht verständlich erklärt: https://www.kuketz-blog.de/firefox-smart-referer-firefox-kompendium-teil6/
Dort steht als Fazit geschrieben: Über welchen Suchbegriff ein Besucher auf eine Webseite gelangt ist oder welche Webseite sich jemand gerade anschaut, mag für einige Protagonisten eine wertvolle Information darstellen. Aus Nutzersicht kann die Sammlung und Auswertung der HTTP-Referer-Informationen allerdings einen Eingriff in die Privatsphäre darstellen, den niemand einfach tolerieren muss. Mittels Smart Referer wird der ursprüngliche HTTP-Referer so umgeschrieben, dass der jeweilige Empfänger daraus keine verwertbaren Informationen extrahieren kann.

Far from smart... Requires a lot of work to un-break all the internet it breaks. (As there is no easy way to add exceptions - and you will need a lot of exceptions.)
Having a UI for that like adblockers do would help. Something that does not require copying URLs into preference-section of the extension.

Great

It used to work fine for me... until the last update. One should never activate "automatic updates"!.
I use Firefox-ESR under Debian Linux 8. After the update, SmartReferer just doesn't send the Referrer to xyz.eu, though i have defined an exception * xyz.eu. I didn't change a thing, a few days ago, it still worked all right. Is there a way to install the old version?

It breaks video playing in facebook. --- 'fbcdn.net/*.mp4' files are blocked by CORS security.

I had a look at the exceptions rules and it already has '*.facebook.com > *.fbcdn.net'. The exception rules are not working anymore? Have to disable to be able to watch videos.

Only way to find out this was the cause of the error was to enable/disable obvious culprits like ublock, decentral eyes, etc.. one by one, and this addon was not at the top of the list.

Does exactly what it says.

There's no telling if this add-on works or not. It doesn't offer any notification of any kind.
I give 2nd star in a good faith that at least it does what it says.

A nice way to keep your navigation private. Thanks for this!

The developer's description of this Fx extension is woefully inadequate.
It fails to explain what the extension does, why and how it does what it does, and (most importantly) what particular issue(s) the extension is designed to address. I ask the developer to please rewrite the description so that it is meaningful to every casual reader (and even to an Fx longtooth [v1.2] and privacy freak who, from the description, has no clue about what this extension is "for").