In zotero/xpcom/attachments.js
  - removed a no longer valid comment from the linkFromURL function

In locale/en-US/zotero/zotero.properties
  - removed a white-space character previously introduced

In zotero/zoteroPane.js linkFromURL function
  - replaced a comment that was previously deleted
  - altered the regex variable urlRe such that the colon was part of the negative lookahead. Still intend to look into implementing other methods of recognizing user input (particularly those suggested by aurimasv)
  - ensured that the user input was had white-space trimmed before proceeding with validation steps