I can’t tell you how much I hate when a web page resizes my entire Firefox window just because they decided to make a web document with a concrete size, normally smaller compared to my window size.
Luckily you can change a “hidden” option in Firefox to prevent that.
This post may sound stupid to some, but there may be people like me that wondered why the spell checking feature of Firefox wasn’t working “out of the box” even when it was enabled in Tools/Options/Advanced.
The truth it’s that the solution it’s quite simple, just go to the add-ons section of Mozilla.org and install all the dictionaries that you want. Once you restart Firefox, the spell checking feature will be working and if needed, you can change the dictionaries on the fly with the Right Mouse Button menu.