Prevent resizing current window
Prevent opening in new window (force to open in new tab)
With this method you can still open a new window by right clicking a link if you want. But it won't allow a new window to be opened when you don't want to, like when clicking on the comments section of a blog. Instead, it will open in the same window in a new tab, and the window will remain the same size.
So I set browser.link.open_newwindow.restriction to 0 and left browser.link.open_newwindow at 3, and it worked like I wanted. Everything opens in new tabs, and my window doesn't ever get resized. I can still open things in new windows if I want via right-clicks, but I prefer always using tabs.