There is a combined Stop/Reload/Go button that is positioned at the right end of the location/address bar.

• Stop button: while the page is loading
• Reload button: when the page has finished loading
• Go button: when you modify the location/address bar content
• Middle-click the Reload button to duplicate the current tab to a new tab

Clear the cache and remove cookies only from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > "Use custom settings for history" > Cookies: "Show Cookies"

You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• Hold down the Shift key and left-click the Reload button at the right end of the location/address bar
• Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)

I usually reload the page using Ctrl+r, and some people like to use F5 (since some other applications use that key), but if you prefer the mouse, it's probably easiest to right-click a blank area of the page and click the circling-arrow icon along the top row of the context menu, versus moving the pointer all the way up to the toolbar.