this.form.valueChanges.subscribe(data => console.log('form changes', data));

<section>
    <div>
        <form [formGroup]="form">
            <fieldset>
                <div class="panel-group m-l-1 m-r-1 accordion vertical-scroll" id="">
                                    <div class="form-group required no-gutter">
                                        <label for="firstname" > First Name:</label>
                                        <div class="col-md-7 col-lg-6">
                                            <input type="text" class="form-control" id="firstname" placeholder="" name="firstname" title="firstname"
                                                formControlName="firstname" size="128" aria-required="true" maxlength="35">
                                        </div>
                                    </div>

            </fieldset>
            <div>
                    <button class="btn btn-primary" type="button" (click)="save()" >Save</button>
                    <button class="btn btn-primary" type="button" (click)="cancel()">Cancel</button>
                </span>
            </div>
        </form>
    </div>
</section>

export class ProfileComponent implements OnInit, AfterViewInit, OnChanges {
    public form: FormGroup;

    constructor(private formBuilder: FormBuilder, private app: Application) {

    }

    loadForm(): void {
        this.form = this.formBuilder.group({
            firstname: [this.app.firstName, Validators.required]
        });
        this.form.valueChanges.subscribe(data => console.log('form changes', data));

    }

    save(): void {

    }

    cancel(): void {

    };

    ngOnInit() {
        this.loadForm();
    }

    ngAfterViewInit() {
        this.loadForm();
    }


}

this.form.valueChanges
.skip(1)
.subscribe(data => console.log('form changes', data));