minor: wrong tooltip on Serialize All Forms

[kitchin]

chrome/content/formbug/FirebugOverlay.xul line 26

- <toolbarbutton label="Serialize All Forms" class="toolbar-text-button" tooltiptext="Populate All Forms" oncommand="Firebug.Formbug.serialize_all_forms()"/>
+ <toolbarbutton label="Serialize All Forms" class="toolbar-text-button" tooltiptext="Serialize All Forms" oncommand="Firebug.Formbug.serialize_all_forms()"/>

[pes10k]

Thanks @kitchin!