facebooktimeline.html

<template>
    <iframe 
        src={facebookSrc} 
        width="340" 
        height="500" 
        style="border:none;overflow:hidden" 
        scrolling="no"></iframe>
</template>

facebooktimeline.js

import { LightningElement ,api, wire} from 'lwc';
import { getRecord } from 'lightning/uiRecordApi';
import FBURL from '@salesforce/schema/Account.Facebook_Page_URL__c';

export default class Facebooktimeline extends LightningElement {
    @api recordId;

    @wire(getRecord, { recordId: '$recordId', fields: [FBURL] })
    Account;

    get facebookSrc() {
        if( typeof this.Account.data !== 'undefined' ){
            return 'https://www.facebook.com/plugins/page.php?href='+this.Account.data.fields.Facebook_Page_URL__c.value+
                  '&tabs=timeline&width=340&height=500&small_header=true&adapt_container_width=true&hide_cover=true&show_facepile=false&appId';
        }
    }
}

facebooktimeline.js-meta.xml

<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata" fqn="facebooktimeline">
    <apiVersion>45.0</apiVersion>
    <isExposed>true</isExposed>
    <targets>
        <target>lightning__AppPage</target>
        <target>lightning__RecordPage</target>
        <target>lightning__HomePage</target>
    </targets>
</LightningComponentBundle>