@Adamano - As per suggestion, we can used it in the <apex:form style="white-space: nowrap;"> like below. It works fine.

<apex:page standardController="contact" extensions="InLineController">
    <apex:form style="white-space: nowrap;">
       <apex:pageBlock title="My Inline Visualforce page">
        <b>Account Name : </b> <apex:outputField value="{!accRec.name}"/><br/>
        <b>Account Number: </b> <apex:outputField value="{!accRec.accountnumber}"/><br/>
         <b>Annual Revenue : </b><apex:outputField value="{!accRec.annualrevenue}"/>
       </apex:pageBlock>
    </apex:form>
</apex:page>

@Admano - As per suggestion, we can used it in the <apex:form style="white-space: nowrap;"> like below. It works fine.

<apex:page standardController="contact" extensions="InLineController">
    <apex:form style="white-space: nowrap;">
       <apex:pageBlock title="My Inline Visualforce page">
        <b>Account Name : </b> <apex:outputField value="{!accRec.name}"/><br/>
        <b>Account Number: </b> <apex:outputField value="{!accRec.accountnumber}"/><br/>
         <b>Annual Revenue : </b><apex:outputField value="{!accRec.annualrevenue}"/>
       </apex:pageBlock>
    </apex:form>
</apex:page>