<PAGE>
                                                                   EXHIBIT 10.25
 
                              EMPLOYMENT AGREEMENT

This Agreement, is entered into by and between XOOM.com, Inc. ("XOOM.COM"), and
Marc Sznajderman ("Employee") and is effective as of December 8, 1998.  XOOM.COM
and Employee agree to the following terms and conditions of employment.

1.  Position and Responsibilities.  Employee is employed by XOOM.COM as Vice
President of Corporate Development and agrees to perform all services
appropriate to that position, as well as such other services as may be assigned
by XOOM.COM.  Employee shall devote his best efforts and full-time attention to
the performance of his duties and shall not accept any other employment or
engage in any other business, commercial, or professional activity that is or
may be competitive with XOOM.COM, that might create a conflict of interest with
XOOM.COM, or that otherwise might interfere with the business of XOOM.COM or any
affiliate.   Employee may serve as a director or as a member of the advisory
board of any company provided that he complies with the restrictions set forth
in Section 1 and Section 4.

2.  Compensation and Benefits.  XOOM.COM shall pay Employee a base salary at the
rate of One Hundred and Twenty Thousand Dollars ($120,000) per year and a
discretionary annual bonus of up to Fifty Thousand ($50,000) to be paid
quarterly upon achievement of personal and company targets to be defined.
Employee will be eligible for an annual review of this agreement no later than
one year from the date of this agreement.

Employee shall receive benefits from all present and future benefit plans set
forth in XOOM.COM's policies and generally made available to similarly situated
employees (as these policies may be amended).  XOOM.COM may, in its sole
discretion, adjust Employee's compensation and benefits provided under this
Agreement.

3.  Termination of Employment.

(a)  By Employer Not For Cause.  Except as modified in section 3(c), below, at
     any time, XOOM.COM may terminate Employee's employment for any reason, with
     or without Cause, by providing one hundred eighty (180) days' advance
     written notice, and shall have the option, in its discretion, to terminate
     Employee's employment at any time prior to the end of such notice period,
     provided XOOM.COM pays Employee an amount equal to the base compensation
     Employee would have earned through the balance of the above notice period
     plus benefits,  thereafter all of XOOM.COM's obligations under this
     Agreement shall cease.  In the event that XOOM.COM exercises its right to
     terminate Employee's employment upon notice under the terms of this
     subsection, Employee shall be immediately entitled to exercise one hundred
     percent (100%) of any stock options granted by XOOM.COM that had not
     previously vested.  If  the stock of XOOM.COM or any parent company is
     publicly traded, Employee's exercise of stock options subject to vesting
     under this subsection must be made within four (4) months of the date upon
     which Employee was informed of XOOM.COM's intent to terminate his
     employment.

                                       1
<PAGE>
 
In the event XOOM.COM's stock is not publicly traded, Employee's exercise of
stock options must be made within twelve (12) months of the date upon which
Employee was informed of XOOM.COM's intent to terminate his employment.

XOOM.COM may dismiss Employee with or without cause notwithstanding anything to
the contrary contained in or arising from any statements, policies, or practices
of XOOM.COM relating to employment, discipline, or termination.

(b)  By Employer For Cause.  Except as modified in section 3(c), below, at any
     time, XOOM.COM may terminate Employee for Cause (as defined below).
     XOOM.COM shall pay Employee all compensation then due; thereafter, all of
     XOOM.COM's obligations under this Agreement shall cease.  "Cause" shall
     include:

       1.  unsatisfactory performance, misconduct, failure to follow policies or
           procedures, material breach of this Agreement, and excessive
           absenteeism. XOOM.COM shall provide at least one appropriate written
           warning of specific deficiencies and provide a reasonable period not
           to exceed thirty days for Employee to cure any such deficiencies.

       2.  to the extent permitted by law, unavailability for work due to
           disability for more than ninety (90) days in any one (1) year period.

       3.  Committing a felony, an act of fraud against or the willful
           misappropriation of property belonging to XOOM.COM.

       4.  Conviction in a court of competent jurisdiction of a felony or
           misdemeanor which adversely and materially affects the ability of the
           executive to perform his duties, obligations and responsibilities
           herein or the good name, goodwill or reputation of XOOM.COM.

(c)  By Employer Following Change in Control or Corporate Transaction.
Notwithstanding the foregoing, in the event that Employee's employment is
involuntarily terminated or Constructively Terminated (as defined herein) by
XOOM.COM, or any successor or assign of XOOM.COM, for any reason, with or
without cause (as defined above), following a Change in Control or Corporate
Transaction or the execution of a letter of intent that, by its terms,
ultimately results in a Change in Control or Corporate Transaction, as those
terms are defined in the XOOM.COM, Inc. 1998 Stock Incentive Plan, Employee
shall be entitled to payment of an amount equal to six months (6) month's base
compensation plus benefits; thereafter, all obligations of XOOM.COM, or any
successor or assign of XOOM.COM, under this Agreement shall cease.   In the
event that Employee's employment is terminated or Constructively Terminated
under the terms of this subsection, Employee shall be immediately entitled to
exercise any and all stock options granted by XOOM.COM that had not previously
vested. "Constructive Termination" shall mean (i) a material reduction in
Employee's salary or benefits not agreed to by the Employee; or (ii) a material
change in Employee's position or responsibilities not agreed to by the Employee;
or  (iii) XOOM.com's (or its successors' or assigns') failure to comply in all
material respects with any material term of this Agreement.

(d)  By Employee.  At any time, Employee may terminate his employment for any
reason, with 

                                       2
<PAGE>
 
or without cause, by providing XOOM.COM thirty (30) days' advance written
notice. XOOM.COM shall have the option, in its complete discretion, to make
Employee's termination effective at any time prior to the end of such notice
period, provided XOOM.COM pays Employee all compensation due and owing through
the last day actually worked, plus an amount equal to the base salary Employee
would have earned through the balance of the above notice period, not to exceed
thirty (30) days; thereafter, all of XOOM.COM's obligations under this Agreement
shall cease.

(e)  Termination Obligations.  Employee agrees that all property, including
tangible Proprietary Information (as defined below), documents, records, notes,
contracts, and computer-generated materials furnished to or prepared by Employee
related to his employment, belongs to XOOM.COM and shall be returned promptly to
XOOM.COM upon termination.  Employee's obligations under this subsection shall
survive the termination of his employment and the expiration of this Agreement.

4.  Proprietary Information.  "Proprietary Information" is all information and
any idea pertaining in any manner to the business of XOOM.COM (or any
affiliate), its employees, clients, consultants, or business associates, which
was produced by any employee of XOOM.COM in the course of his or her employment
or otherwise produced or acquired by or on behalf of XOOM.COM.  Proprietary
Information shall include, without limitation, trade secrets, product ideas,
inventions, processes, formulas, data, know-how, software and other computer
programs, copyrightable material, marketing plans, strategies, sales, financial
reports, forecasts, and customer lists.  All Proprietary Information not
generally known outside of XOOM.COM's organization, and all Proprietary
Information so known only through improper means, shall be deemed "Confidential
Information."  During his employment, Employee shall use Proprietary
Information, and shall disclose Confidential Information, only for the benefit
of XOOM.COM and as is necessary to perform his job responsibilities under this
Agreement.  Following termination, Employee shall not use any Proprietary
Information and shall not disclose any Confidential Information, except with the
express written consent of XOOM.COM.  By way of illustration and not in
limitation of the foregoing, following termination, Employee shall not use any
Confidential Information to compete against XOOM.COM or employ any of its
employees.  Employee further agrees that for one (1) year following termination,
he shall not solicit any customer or employee of XOOM.COM.  Employee's
obligations under this Section shall survive the termination of his employment
and the expiration of this Agreement.

5.  Integration and Amendment.  This Agreement is intended to be the final,
complete, and exclusive statement of the terms of Employee's employment.  This
Agreement supersedes all other prior and contemporaneous agreements and
statements, whether written or oral, express or implied, pertaining in any
manner to the employment of Employee, and it may not be contradicted by evidence
of any prior or contemporaneous statements or agreements.  To the extent that
the practices, policies, or procedures of XOOM.COM, now or in the future, apply
to Employee and are inconsistent with the terms of this Agreement, the
provisions of this Agreement shall control.

This Agreement may not be amended except by a written agreement signed by each
of the 

                                       3
<PAGE>
 
parties. Failure to exercise any right under this Agreement shall not constitute
a waiver of such right.

6.  Interpretation.  This Agreement shall be governed by and construed in
accordance with the law of the State of California.  This Agreement shall be
construed as a whole, according to its fair meaning, and not in favor of or
against any party.  By way of example and not in limitation, this Agreement
shall not be construed in favor of the party receiving a benefit nor against the
party responsible for any particular language in this Agreement.  If a court or
arbitrator holds any provision of this Agreement to be invalid, unenforceable,
or void, the remainder of this Agreement shall remain in full force and effect.
Captions are used for reference purposes only and should be ignored in the
interpretation of the Agreement.

7.  Acknowledgment.  Employee acknowledges that he has had the opportunity to
consult legal counsel in regard to this Agreement, that he has read and
understands this Agreement, that he is fully aware of its legal effect, and that
he has entered into it freely and voluntarily and based on his own judgment and
not on any representations or promises other than those contained in this
Agreement.

8.  Successors and Assigns.  This Agreement shall be binding upon, and inure to
the benefit of and shall be enforceable by the respective successors and assigns
of the parties hereto, as well as the Employee's heirs, executor or
administrator.

9.  Waiver, Modification or Amendment.  No amendment of, or waiver of any
obligations under this Agreement will be enforceable unless set forth in a
writing signed by the party against which enforcement is sought.


The parties have duly executed this Agreement as of the date first written
above.


EMPLOYEE                               XOOM.COM, INC.



---------------------------------      ---------------------------------      
By:                                    By:   Laurent Massa
                                       Its:  President and CEO

                                       4