Does it happen on this site (I have en-US in mixed case in the URL)?

Mine's still working fine. I have Firefox 11 on Windows 7 Professional (64-bit) with Outlook 2010 and default mail format is HTML with blank stationery.

Office's AutoCorrect and AutoFormat as You Type features can sometimes modify text unexpectedly. However, nothing comes immediately to mind to turn off.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.org/kb/Safe+Mode

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Yes, still happens; it changed the 'US' to 'us" in the link it put in Outlook for this page.

To reset Firefox's external mail handler settings, could you try this:

orange Firefox button or classic Tools menu > Options > Applications

In the search box, type or paste mailto and pause while the list is filtered.

Then choose one of the non-Outlook options, save, and OK out of Options.

Then repeat the steps and change it back.

Any change in the symptoms?

Unfortunately, it did not work. I thought for sure that it would because it seemed so creative. Interestingly, I sent an upper/lowercase link by GMail and it worked correctly. BUT, when I changed back to Outlook 2007, that same link was all in lower case when sent by Outlook. Thanks for the suggestion.

Try to delete the mimeTypes.rdf file in the Firefox Profile Folder.

• http://kb.mozillazine.org/mimeTypes.rdf
• http://kb.mozillazine.org/File_types_and_download_actions#Resetting_download_actions

You can use this button to go to the Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Open Containing Folder

Thank you cor-el! That fixed it.