ROPES & GRAY
                            One International Place
                          Boston, Massachusetts 02110

                                                                   Exhibit 5.1

                                 June 24, 1996


FTP Software, Inc.
100 Brickstone Square, Fifth Floor
Andover, Massachusetts 01810

Ladies and Gentlemen:

     This opinion is furnished to you in connection with a registration
statement on Form S-4 (the "Registration Statement") filed with the Securities
and Exchange Commission (the "Commission") under the Securities Act of 1933, as
amended, for the registration of 7,650,000 shares of common stock, $0.01 par
value per share (the "Shares"), of FTP Software, Inc., a Massachusetts
corporation (the "Company").  The Shares are to be issued in exchange for shares
of common stock, $0.001 par value per share, of Firefox Communications Inc.
("Firefox") pursuant to an Amended and Restated Agreement and Plan of Merger
dated as of May 21, 1996 (the "Merger Agreement") among the Company, Firefox and
Firefox Acquisition Corp., as wholly-owned subsidiary of the Company and a
Delaware corporation ("Sub").  The Merger Agreement provides for Sub to merge
with and into Firefox (the "Merger") and for Firefox to survive the Merger as a
wholly-owned subsidiary of the Company.

     We have acted as counsel for the Company in connection with the issuance of
the Shares pursuant to the Merger.  For purposes of our opinion, we have
examined and relied upon such documents, records, certificates and other
instruments as we have deemed necessary.

     Based upon the foregoing, we are of the opinion that the Shares being
issued by the Company have been duly authorized and, when issued in accordance
with the Merger Agreement, will be fully paid and nonassessable.

     We hereby consent to the filing of this opinion as part of the Registration
Statement and to the use of our name therein and in the related joint proxy
statement/prospectus under the caption "Legal Matters."

 
     This opinion is to be used only in connection with the issuance of the
Shares while the Registration Statement is in effect.

                                             Very truly yours,
                                    
                                    
                                             Ropes & Gray