changing font size on Firefox

I'm having trouble getting my font size to stay at the size I want it too.
I'm using Firefox 3.0 on this new computer. I like 3.0 better than the 5.0 that I tried.
the problem I'm having is more specifically for twitter. I know I can use ctrl+ to make the font bigger and the page wider on my page. but when I refresh the page, it goes back to the smaller size font and page layout. I know you can go under Tools/Options/Content/Font&Colors, but that's the same as I had on my old computer(Times New Roman/16) where I could get the page to stay at the bigger size on twitter.
hope I'm explaining this right, any help?

 

solved it myself.

under Tools/Options/Privacy I had Firefox to start Firefox automatically in private browsing session. I changed that, and since then pages load in the previous font.layout that I had them on.