(I don’t know/tested any of these.)
There are some Firefox add-ons that might help here:
- Long URL Please Mod
- Long URL Please (uses the service http://www.longurlplease.com/)
- LongURL Mobile Expander (uses the service http://longurl.org/)
There are also userscripts:
- LongURL Mobile Expander
- Untiny (uses the service http://untiny.me/)