What version of Windows and Office is it? I had this issue with an older version of office and Windows XP. Basically, MS are using their browser (IE) because it's their software (MS Office). If you go to options in MS word though, you should be able to find an option to set the default browser to open links.

I'm using MS Office 2003 on a laptop with Windows XP Pro SP3. I don't know how to force MS Word to open a link in Firefox, but I'm sure that opening links in Firefox (my default browser) from MS Word was the normal behaviour until few days ago.

The problem has been solved. It was just a problem of filetype association: the filetypes .htm and .html were associated to MS iExplorer (I don't know why!). I have changed the association to Firefox and now everything is OK.

Well done!

Thank you!!!

I have the same problem, but the difference is in opening MS WORD hyperlinks to download documents (for example http://ntv.spbstu.ru/2011/hss_2011_3.pdf#page=145 ). This link wants to call MS IE. At the same time all HTML links are opened in FireFox.