I would like Word to open links in Firefox instead of Chrome

I would like Word to open links in Firefox instead of Chrome, but I only get two options - no browse button ...

I think Firefox would need to be your default browser.

Here is how to make it your default, if you choose to make it so:
Default browser - MozillaZine Knowledge Base

Maybe this will help then:
How to Change the File Associations in MS Word 2010 | eHow.com

When I use the following path, I have the option to change the program for the file type extension:

Control panel / Programs / Make a file type always open a specific program / then select the file extension. On the top right-hand side is a button labelled 'Change', after this point, the recommended programs are listed and a browse button on bottom right. Do you not get this option?
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Look in Control Panel\Default Programs -> Set Associations
sort your list by Current Default
look for anything associated with chrome
change what you need to firefox

It's probably .url (Internet shortcut) that associates links in Word but I'm not certain.

Did that work?

As for the extensions: I have no defaults set for Google Chrome. I've taken a look at the program associated with the .url extension and it was 'Internet Browser' (with 'Microsoft Corporation' underneath that). I changed that to Mozilla Firefox and again tried to open a link in Word, hoping this time it would launch Firefox, but it didn't.
The only things I have associated with Google Chrome are two protocols: 'MAILTO' and 'WEBCAL'; none of which I can change - whichever protocol I want to change, I never get a 'Browse...' button as when clicking the extensions.
Compare the left window (when clicking an extension to change it) to the right ( ~ protocol ~)

thanks!