Check the Mailto application in Tools > Options > Applications

Make sure that it isn't set to the Firefox program.

See also:

• Firefox repeatedly opens empty tabs or windows after you click on a link

hi cor-el, i checked and it's set to "use windows live mail (default)" when it starts opening tabs it's really aggressive - when you close it, it just keeps re-opening it's self untill you press "ctrl alt del" to open task mgr and "end task". if you try to shrink the page it just re-opens. i run a scan using malwarebytes once a week and nothing shows up. also run AVG scan but again nothing. ta for any help you can give

You can look at the network.protocol-handler.external.mailto prefs on the about:config page.
If network.protocol-handler.external.mailto prefs are user set (bold) then right-click and Reset them to the default value.
You can also try to change the network.protocol-handler.warn-external.mailto pref to true.

To open the about:config page, type about:config in the location (address) bar and press the "Enter" key, just like you type the url of a website to open a website.
If you see a warning then you can confirm that you want to access that page.