All of a sudden, whenever I click on a link in an email (I'm using Thunderbird), the web page opens up in IE instead of in Firefox like it has been doing for the last two years.

I didn't make any changes to anything.

How do I fix this???

First check Firefox is still the default browser -

Tools/Options/Main/"Check if Firefox is default"

If it already is the default, -

Open Windows Explorer or My computer.

Tools | Folder Options | File Types.

Scroll down to URL:HyperText Transfer Protocol and select it.

Click Edit or Advanced, depending on your Windows version.
Select 'open'. Click Edit.

"Application used to perform this action" should read:

"C:\Program Files\Mozilla Firefox\firefox.exe"

(Check the path to Firefox to make sure that is correct and use the
double quotes.) DDE should be checked.

I had a feeling it was something simple, but I didn't know what.

Thanks very, very much!