Can you go into Customize mode to check on whether the icon moved to another bar, or fell off all the bars? Either:

• right-click a blank area of the tab bar > Customize
• tap the Alt key > View menu > Toolbars > Customize

All toolbars should be visible, even the ones you normally don't show. Unused icons may be in the Customize dialog where you can drag them to your preferred location.

Any luck?

If that fails, reset the localstore.rdf file (resets toolbar layout and fixes other issues).

• Read: http://kb.mozillazine.org/Corrupt_localstore.rdf

tried both of those before posting the issue :(

I looked into this a little further. The Springpad extension has been withdrawn from the add-ons site, and Springpad launched a new extension named Springpad Clipper.

According to the versions page for the old Springpad extension (in Google cache), as of 8/23/2013, this was posted by Springpad on 12/21/2012:

"This is the last version that we plan to release of this Springpad Firefox add-on. ... In the near future, we will release a new clipper-based add-on. At that point, we urge you to begin using the new clipper add-on along with the web app at Springpad.com, where we will continue to make frequent upgrades to support all of our users."

More info on the change:

• Springpad Browser Extensions: New Clipper Extension to Replace Older Features - Springpad blog
• https://addons.mozilla.org/en-us/firefox/addon/springpad-clipper/

You may need to disable the old (apparently broken) extension to avoid a conflict with the new one. You can do that here:

orange Firefox button (or Tools menu) > Add-ons > Extensions category

Thank you I've installed the new add-on and it works :)