As you may already know, the Mozilla-developed web browser warns you when you make a spelling mistake. By default, Firefox puts a squiggly red line underneath the misspelled word. The catch is that the squiggly line is not that visible; you could go over your text and miss the spelling error. Luckily enough there is a cool trick you can use to make spelling errors more visible.
Here is what you have to do. Follow the step by step instructions presented below.
Step 1. In the URL bar type in about:config and press Enter. When the This might void your warranty prompt shows up, just click I’ll be careful I promise.
Step 2. Now you have to search for ui.SpellCheckerUnderlineStyle; you can do so by pasting ui.SpellCheckerUnderlineStyle in the Filter box. But chances are that you will not find anything. So what you have to do is create a new integer. To do so, right click anywhere underneath the Filter box -> click New -> then click Integer.
Step 3. When the New Integer Value window shows up, type in (or paste) ui.SpellCheckerUnderlineStyle
Step 4. A Enter Integer Value window will show up. You can enter a value from 0 up to 5.
Enter 0 and Firefox will no longer highlight spelling errors. Enter 1 and Firefox will put a dotted line underneath spelling errors. Enter 2 and Firefox will put long dots underneath spelling errors. Enter 3 and Firefox will put a single straight line underneath spelling errors. Enter 4 and Firefox will put double lines underneath spelling errors. To my mind this is the best option as it better highlights spelling mistakes.
SPONSORED LINKS
Enter 5 and nothing will change; Firefox will continue to put the default squiggly line underneath spelling mistakes. You can try them all out if you want. Simply right click ui.SpellCheckerUnderlineStyle -> select Modify. When the Enter Integer Value shows up, enter a value between 0 and 5, then hit Enter or click OK.
In related news, the latest Firefox version is Firefox 3.6.6. You can download the browser here.
As you may already know, the Mozilla-developed web browser warns you when you make a spelling mistake. By default, Firefox puts a squiggly red line underneath the misspelled word. The catch is that the squiggly line is not that visible; you could go over your text and miss the spelling error. Luckily enough there is a cool trick you can use to make spelling errors more visible. 
