Dear JoKalliauer, I can not support your counter-proposal for new fonts. It doesn't do justice to all the benefits of the request for adding Fira Sans, which is based on it's excellent characteristics for usage on the Internet and the fact is has a really large character set including text figures and small caps. We need Fira Sans for it's readability when used in images that are shown as thumbs.

Thank you for this proposal! It has my support.

Thanks for your help. I will follow that new path.

Disabling the default (Vector) skin of the Commons interface solves the error.
See: https://commons.wikimedia.org/wiki/Special:Preferences

No problem.
I can not open the View History tab to purge the webpage, so I used https://commons.wikimedia.org/wiki/File:King_William_II_of_the_Netherlands_in_1840.png**?action=purge**

I tried disabling Adblock Plus on https://commons.wikimedia.org/wiki/Special:UploadWizard
Then I did a browser refresh.
-> This made the Flick button disappear, as well as it enabled me being able to use the Select Mediafiles button.
You may like to know which filter subscriptions I have (with the respective homepages provided by Ad Block Plus) :

• EasyList https://easylist.adblockplus.org/en/
• EasyPrivacy https://easylist.adblockplus.org/en/
• Malware Domains http://www.malwaredomains.com/?page_id=2
• Fanboy's Social Blocking List https://easylist.adblockplus.org/en/

Ofcourse the fact that a "simple" browser add-on can (accidentally) make a feature available to me that I shouldn't have access to, raises some concern about the vulnerability of Commons Wikimedia.

Hi, the debug link you provided doesn't give me any error reports.
I'm still not able to use the select files button on page https://commons.wikimedia.org/wiki/Special:UploadWizard
It still produces an error message like above.
Wouldn't it be wise to do a roll-back on the introduction of the Flickr button until the problem is solved ?
Using folks like me as unsolicited beta-testers is not a good idea, i.m.o.
I'm willing to help out and test stuff, provided it's optional and I can still continue with my projects.
Surely you can use an unofficial variant of this page to work on the new Flickr button and leave the old page in place until work is finished ?
Just my thoughts.

Nothing happened when clicking the button, but there is this even before doing so:

PS: I did receive some additional rights recently. I'm now a member of the autopatrollers. And I'm surfing with Cyberfox 35.0 a 64-bits browser built on Firefox (with Gecko).

An other screen showing waht happens when I click on the Flickr button.

Thanks for the help.
A screen of the problem:

I would appreciate a reply to confirm I created a bug-report the correct way.