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A protocol is the part of a web address before the colon. For example, web pages are normally http or https protocols. If you click on a link that specifies a protocol other than http: or https: (such as aim:goim?screenname=MozillaSupport), you may receive an error message like:
Firefox doesn't know how to open this address, because the protocol (aim) isn't associated with any program.
These type of links are most commonly used to launch external programs. For example, clicking on an aim: link should open an AOL Instant Messenger client window. The error message is telling you neither Firefox nor any program Firefox knows about can handle the protocol.
These errors can occur with any protocol other than the ones Firefox handles itself, and commonly occur with:
- aim - Starts an AOL Instant Messenger chat.
- msnim - Starts an MSN Messenger/ Windows Live Messenger chat.
- mailto - Starts your normal e-mail service.
Table of Contents
Determine what program should run
The context in which the link that causes the error appears should make the expected behavior obvious. For example, a web page for a friend might have a link labeled "MSN Screen Name" that causes the error. In this case, an MSN/Windows Live Messenger client should start.
Once you have determined which program should run:
- For mailto errors: See Change the e-mail program used by Firefox for instructions on how to make Firefox use your standard e-mail program or service.
- For msnim errors: Skip to the Associate the protocol with a program in Firefox section below.
- For other protocols: Follow the instructions below.
Re-install the program associated with the protocol
Try re-installing the latest version of the program that is supposed to handle the protocol that is causing the error. For example, if aim links fail, you might re-install the AOL Instant Messenger/AIM program from http://www.aim.com. Re-installing may correct the issue.
Register the protocol in Firefox
Firefox gets its protocol information from its hidden settings.
- Type about:config in the address bar and press EnterReturn.
A warning page may appear. Click to continue to the about:config page.
- Right-clickHold down the Ctrl key while you click anywhere in the grid, choose , then .
- In the Enter the preference name prompt, type in network.protocol-handler.app.myprotocol (replacing myprotocol with the protocol you want to register) and press .
- In the Enter string value prompt, type the path to the program you want the protocol to start and press .
Now that the protocol has been registered, try the link again. You may get an External Protocol Request dialog. Click. The program you chose should now start.
- Make sure that the path you put in the preference is correct. Due to a bug in Firefox, entering an incorrect path will give you the same error message.
Associate the protocol with a program in Firefox
If re-installing the program that should handle the protocol does not work, you can try to set Firefox to associate the protocol to the program.
First, register a new Protocol Handler in Firefox:
- Copy the code below:
- For aim links:
- For msnim:
- For other protocols, change the protocolName to match the name of the protocol you want to register and programName to the name of the program you want to have open:
- For aim links:
- While still on this Knowledge Base article, click on the Location bar to highlight the web address (URL) of the current page. Paste the code you copied into the Location bar, replacing the current text.
- After you paste the code into the Location bar, press EnterReturn. Firefox's information bar will appear, asking Add programName (support.mozilla.com) as an application for protocolName links?
- Click on
on the Information bar.
Next, associate a program with the protocol:
- Return to the website with the link that caused the original error. When you click on the link now, the Launch Application window will appear instead of the error message.
- In the Launch Application window, click to select Choose an Application and then click on .
- Use the open file window to select the program you want to run.
- For the msnim protocol: Navigate to C:\Program Files\Internet Explorer and select iexplore.exe.
- Some programs only register themselves with Internet Explorer, so Firefox can use Internet Explorer to cause the correct program to launch, as with msnim above.
- After selecting the program you want to run, click .
If the steps above work, you can select Remember my choice for protocolName links in the Launch Application window the next time you click on a link for the protocol.
If the steps above do not work, contact the vendor for the program you want to have run when you click on links for the protocol. That program may need special system-level changes to open its protocol links from external programs.
Based on information from Register protocol (mozillaZine KB)