If you frequently examine the source code of web pages while using Firefox, this handy trick will load the source code directly in your favorite editor.
Load your Firefox configuration file by typing about:config in the address bar, and follow these steps:

• Type or copy & paste "view_source.editor.external" (without the quote marks) into the filter address bar. Once the about:config entry is displayed, right click on the entry and select "Toggle" to change the value to "true".
• Type or copy & paste “view_source.editor.path” (without the quote marks) into the Filter Address Bar. Once the about:config entry is displayed, right click on the entry and select “Modify”.
• Enter the target path of your favorite code/text editor (without the quote marks). For example, chosen “C:\Windows\System32\notepad.exe”. Click “OK” and restart your browser to complete the changes.

Now, whenever you view source code from within Firefox, your favorite code/text editor will open up displaying all that webpage code. (via The How-To Geek)

Tips to Speed Up Your Firefox

Updated: Firefox 3.5 extremely slow on startup? [Win] Try to go to the schortcut of firefox, put this in the target tab /Prefetch:1

Like this : "C:\Program Files\Mozilla Firefox\firefox.exe" /Prefetch:1 (Make sure you have space in between firefox.exe” and /Prefetch:1)

Or, check this: Workaround for Firefox 3.5 slow startups on Windows