Each time you make use of the "Save Link As" under Firefox, you have a certain amount of time to proceed before getting a connection timeout error.
To increase this delay:
- In the address bar type "about-config" and press Enter
- In the Filter field search for "Browser.download.saveLinkAsFilenameTimeout"
- Double click on this entry to set the value from 1000 miliseconds (1 sec) to 10000 (10 seconds)
- Close the about: config window