Maybe what's mentioned here applies to your situation  ?

https://discourse.mozilla.org/t/no-install-button-on-add-on-page/28908

McCoy said

Maybe what's mentioned here applies to your situation  ? https://discourse.mozilla.org/t/no-install-button-on-add-on-page/28908

McCoy said

Maybe what's mentioned here applies to your situation  ? https://discourse.mozilla.org/t/no-install-button-on-add-on-page/28908

Thank You this is the solution!!!

"On the bottom of the add-on page of Mozilla is a link to the desktop site. After changing to this version I had the d/l link. Hope this helps others with same problem"

But why mozilla offers a wrong Site?????

Your browser gave this forum a very unusual identification:

Mozilla/5.0 (Windows NT 6.1; Win64; x64; WOW64; rv:41.0) Gecko/20100101 Firefox/61.0.2 (x64 de) Anonymisiert durch AlMiSoft Browser-Anonymisierer 70719903

Usually Win64 and WOW64 do not occur together because one indicates 64-bit Firefox and one indicates 32-bit Firefox on 64-bit Windows. Usually rv:41 and Firefox/61 do not occur together because those versions should match. And of course the rest of it... ???

For comparison, this is my useragent string with Windows 7 and 64-bit Firefox 61:

Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:61.0) Gecko/20100101 Firefox/61.0

Perhaps the inconsistencies were confusing to the Add-ons site??

To clear optional settings for your Firefox user agent string, see this article: How to reset the default user agent on Firefox. However, it's possible that your proxy or whatever that software is may be modifying it "in flight" between Firefox and the site.

You can test on my page here (look for the red text): https://www.jeffersonscher.com/res/jstest.php

It seems the problem is the part after the Firefox/61.0 or Firefox/61.0.2. If I experiment, this works (blue install button):

Mozilla/5.0 (Windows NT 6.1; Win64; x64; WOW64; rv:999.0) Gecko/20100101 WHATEVER Firefox/61.0

But this doesn't:

Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:61.0) Gecko/20100101 Firefox/61.0 Hi

I guess the newer version of the site checks that last part of the user agent string differently than the "Classic" version of the site.

Nothing changed there is no blue button (!) to install

I only have one of the useragent (see jpg) and made a reset. The recent "red lines" are now:

Browser "User Agent" string: Mozilla/5.0 (Windows NT 6.1; Win64; x64; WOW64; rv:41.0) Gecko/20100101 Firefox/61.0.2 (x64 de) Anonymisiert durch AlMiSoft Browser-Anonymisierer 77537959

navigator.userAgent = Mozilla/5.0 (Windows NT 6.1; Win64; x64; WOW64; rv:41.0) Gecko/20100101 Firefox/61.0.2 (x64 de) Anonymisiert durch AlMiSoft Browser-Anonymisierer 77537959

before it was rv:999 now: rv:41 but no rv:61 ....

Note that even the slightest addition to the Firefox user agent after Firefox/xx.x.x makes the Addons website fail to recognize Firefox. Only a clean user agent works properly.

But what is the complete way to clean it?? What is wrong? I reset only "generel.useragent.overide" the result is above. What shall I do anyway?

Does "AlMiSoft" (https://almisoft.de/) seem like something you would be running on your computer or have a subscription for?

i´ve deinstalled now Almisoft. Now the useragent is clean!! AND the blue install button is working! The Problem is solved now!

THX MUCH!!

CLB3107 said

i´ve deinstalled now Almisoft. Now the useragent is clean!! AND the blue install button is working!

If you want to use that software, I would check with their support on how to avoid the extra text in your user agent string. If anyone is concerned about "fingerprinting," something so unique is not desirable.