Font size is irratic

I thought that I posted this in the last week or so. 
 I normally use font size 10, however, sometimes I start a new line of text and the size is 8 
 sometimes when I add to an existing line of text that is in size 10, it will insert the new text in size 8
 another annoying thing with font size sometimes occurs when I do a search, it will display some lines of text in a size that is too small for the naked eye to read; in fact, I would like to know how to select that ultr-small size because I would use it under certain conditions .
  
 on another subject, I find this new Yahoo group format very hard to navigate. I don't know why Yahoo changed it.