Proposal to rework the nav:
Accueil (Home) --> should'nt be in the nav. Just access it by clicking on the logo.
Rechercher (Search) --> shouldn't be a tab. Just make a field always visible in the header.
Contact --> This goes in the footer. Remove the text, just keep the e-mail addresses and logos.
About & Start --> could both be in the front page with an accordion (who doesn't love accordions ?) I tend to think it's better to have everything being displayed rather thant clicking on several tabs until you find whatever you were looking for.