Unfortunately, I do not understand which error you are getting.

Is this a message on a bar with an Allow button, or a full page error, or an error on the download list?

Could you possibly post a screen shot, or copy/paste what you see?

You ask me for a screen-shot, so I posted it here. the retry button (opnieuw proberen) does nothing at all.

The translation is " this adress has restricted acces"

Does the address contain an unusual port number, after a colon, such as:

example.com:9876

You can create a preference using about:config and allow the port number which Firefox is blocking. Please see:

http://www.mozbrowser.nl/forum/viewtopic.php?p=59811

In English:

(0) Select and copy the following preference name

network.security.ports.banned.override

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste ports and pause while the list is filtered

If the above-listed preference exists:

(3) Double-click it and add a comma to the end of the list followed by the port number you need to allow. No spaces. Then click OK.

If the above-listed preference does not exist:

(4) right-click anywhere on the page and choose New > String

(5) In the preference name dialog, paste the name you coped and click OK

(6) In the preference value dialog, type in the port number you need to allow, then click OK.

Thanks for the help, it now runs smoothly