SVG font size difference between Firefox and Adobe SVGviewer

In order to view SVG pictures coming from Visio, I used this list to
find out I had to change the DOCTYPE and add the xmlns:xlink before
they were visible in Firefox. After this change they were still
visible in IE7 with SVGviewer, so looked to be cross-browser
compatible.

The problem is that in Firefox the font is too large, overflowing the
defined boxes, even though it is specified with a unit. By
experimentation I found out I had to divide the font size by 1.4
(0.666664em --> 0.476em) to make the text mimic the size it had in
IE7. But when I reloaded the SVG in that browser, there too the texts
were shrunk, to a too-small font.

Is there a way to specifiy the text size in SVG such that the font
size in Firefox and IE7 looks the same?

Part of Visio output:

<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.0//EN" "http://www.w3.org/TR/
2001/REC-SVG-20010904/DTD/svg10.dtd">
<!-- Generated by Microsoft Visio 11.0, SVG Export, v1.0 i38346.svg
400/16_450/20 -->
<svg xmlns="http://www.w3.org/2000/svg" xmlns:v="http://
schemas.microsoft.com/visio/2003/SVGExtensions/"

		.st4 {fill:#000000;font-family:Arial;font-size:0.666664em}


My changes:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
         "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg
   xmlns="http://www.w3.org/2000/svg"
   xmlns:xlink="http://www.w3.org/1999/xlink"
   xmlns:v="http://schemas.microsoft.com/visio/2003/SVGExtensions/"

		.st4 {fill:#000000;font-family:Arial;font-size:0.476em}