When I set a minimum font size in prefs and then view a SVG graphic which is scaled, the font sizes are very wrong. In the example I will attach, I use the SVG coordinate system of 1 day per "unit", and then scale the viewBox so that the chart makes sense. This forces the fonts extremely large. We should either ignore the minimum font size when displaying SVG, or make it apply after all scaling is complete.
I have found something similar, however it basically is solved in beta 3 and Minefield. They get it wrong in other ways though. My findings are at http://keryx.se/dev/svg/geckobug-08-01/
Fixed a long time ago by bug 358032