One of the most prominent Firefox annoyances often happens when you try to select a portion of text. Most of the time, some unwanted portion of adjacent text also gets selected, making you start the selection process again.
What many do not know is that you can enable Word or Notepad style mouse caret (the vertical blinking mouse cursor) in Firefox, using which more precise selection of text can be done.
Just hit F7 button while in Firefox and it'll ask you whether you want to enable caret mode. Select yes and you get a nice blinking cursor on screen. Using this cursor you can select text the traditional way - click and drag with mouse, arrow keys, Ctrl + arrow keys to highlight words etc.