[FIX] “The Address Wasn’t Understood” Error In Mozilla Firefox

If you're having trouble opening any website in Firefox due to error "The address wasn't understood'' error, then here is how to fix it.

Kapil Arya
11x Microsoft MVP · Admin
2 min read
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Mozilla Firefox like other competing browsers, can understood various kind of network protocols for example, FTP, HTTP, RSTP etc. But if the protocol setting of Firefox is either disturbed or malfunctioned, it may have trouble understanding the protocol you’re requesting. The protocol setting of Firefox could be affected due to harmful content inside cookies or cache, thrown by the websites you visit. Additionally, the add-ons you use could also change the protocol settings. Recently, I came around following error while using Firefox, even with HTTP addresses:

The address wasn’t understood

Firefox doesn’t know how to open this address, because one of the following protocols (javascript) isn’t associated with any program or is not allowed in this context.
You might need to install other software to open this address.

After receiving this error, the first thing I did was restarting Firefox, but no change in the situation. Secondly, clearing cookies and cache too didn’t helped in my case. At last, I tried to change the advance protocol handling settings, and this finally fixed the problem. Hence, I am sharing the cure to this issue, with you guys:

FIX : “The Address Wasn’t Understood” Error In Mozilla Firefox

1. Open Mozilla Firefox window, type about:config in the URL bar and hit Enter key. Click I’ll be careful, I promise! option now.

FIX Unable To Block Pop up Windows In Mozilla Firefox 1

2. In the Search filter, type network.protocol-handler.external.javascript and you’ll be resulted Preference named network.protocol-handler.external.javascript which is set to true, actually it is the root cause of this problem. All you need to do is to double click on this Preference Name to set its Value to false which is the default value.

You can now close Firefox and restart it, the problem should be fixed on the go.

Hope this helps. Do checkout about:config tricks for Firefox!

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Article by

Kapil Arya
11x Microsoft MVP · Admin

Kapil holds Microsoft MVP title in Windows IT Pro expertise, 11-times in a row (2014-2025). He is 8-times Windows Insider MVP as well, and author of 'Windows Group Policy Troubleshooting' book. In 2015, Microsoft India accomplished him as 'Windows 10 Champion'. Being passionate Windows blogger, he loves to help others on fixing their system issues. Kapil has worked with official Microsoft Community Engagement Team (CET) on several community projects. You can subscribe him for news/updates and fixes for Windows.

guzbiz

thank’s … god job! manteb om …. xixixixi

Geoff

Did not work as it was already set to false

dobetter

same as geoff worthless advice

Cipriana

Didn´t work. It was already set to false.

Reza

hello , i have simillar problem :
Firefox doesn’t know how to open this address, because one of the following protocols (tg) isn’t associated with any program or is not allowed in this context.

You might need to install other software to open this address.
what can i do to solve the problem.

inalzninz

mine is not (javascript) its (loaditem) please solve this error

edsel

thankz i use mozilla firefox now

Kapil Arya Author

^^ 👍

AHN

Didn’t work. It was already set to false, And the software is already installed

Joanne Green

I use my computer for entertainment instead of cable or satellite. EVERY time I sign in to google through BING; FIREFOX I get this confusing message. Just recently. I don’t have time to trouble shoot every night when time is precious.
Can I not just go back to last week’s settings when I could access you tube without problems\/

Thanks,
JG

Ray D

You could use the hammer approach and go to the library icon on the top right of the page, select history then clear history. You will be presented with an option to clear history from different time periods or all history. I just cleared all history and it worked. Didn’t have time to find out which particular item was causing the problem.

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