Grid fixedLayout inside vbox fails on FireFox

<window>
	<vbox>
		<grid fixedLayout="true">
			<columns>
				<column label="Brand" width="100px" />
				<column label="Processor Type" width="150px" />
				<column label="Memory (RAM)" width="120px" />
				<column label="Price" width="100px" />
				<column label="Hard Drive Capacity" width="150px" />
			</columns>
			<rows>
				<row>
					<label value="Dell E4500 2.2GHz" />
					<label value="Intel Core 2 Duo" />
					<label value="2GB RAM" />
					<label value="$261.00" style="color:green" />
					<label value="500GB" />
				</row>
				<row>
					<label value="XP-Pro Slim Dell-Inspiron-530-s" />
					<label value="Intel Core 2 Duo" />
					<label value="2GB RAM" />
					<label value="$498.93" style="color:green" />
					<label value="500GB" />
				</row>
			</rows>
		</grid>
	</vbox>
</window>