Hi. Laura. My name is***** you for your question and the opportunity to assist. Try doing a refresh of Firefox
to see if that clears this up. (you'll need to reactivate the pinterest toolbar afterwards)
In Firefox, click the 3-horzontal-bar icon in the upper right corner and click on the ? at the bottom.
From that menu select Troubleshooting Information. Click Refresh Firefox (twice)
When the operation is complete Firefox will reopen. Add pinterest back and let me know the result please.
If it's still not working, there was an update to the share button that came out last week.
You can get that here: https://addons.mozilla.org/en-US/firefox/addon/pinterest-pin-button/
There's no guarantee that an update would have fixed things. Refreshing Firefox keeps it running optimally.
Right-click on the 3 bar icon and and select Menu Bar such that it now has a checkmark next to it and is visible on the page.
Right-click again and do the same for Bookmarks Toolbar.
Left click the 3 bar icon and select Add-ons. Click Extensions on the left side of the page and enable anything you had previously.
Click the 3 bar icon again and select Options. From the menu on the left you can make changes.