I´m dealing with SVG file in order to make some realtime animations on browser using AJAX.
Everything is fine except to make the browser (Chrome or IE9) to show the
The SVG 1.2 Full specification was never completed (as you can see from the link it's still in draft from 2005) and only Inkscape ever supported flowRoot I think. I don't think it's intended that flowRoot will be part of SVG 2 either as that is likely to implement flowing text with a different and more CSS compatible mechanism so flowRoot is best avoided.
Use the Convert to text" command in the Text menu to convert it to SVG 1.1 compliant text.
As others have said, you can use convert to text or unflow to remove the flowRoot.
Keep in mind however that the text will no longer stay within the boundary you specified.
To avoid flowRoot going forward, just click with the text tool and start typing rather that first dragging to set a bound for it.
To creat text that fits within a bounding box, I'm not sure what the best method is.