Reload Plus makes the following (user-configurable) changes to the behavior of Firefox's "Reload" button:
Left Mouse (or F5) = Standard Reload
Ctrl+LMouse (or Ctrl+F5) = Override Cache
Alt+LMouse (or Alt+F5) = Load Missing Images
Shift+LMouse (or Shift+F5) = Google Cache
Middle Mouse = Standard Reload (new tab)
Ctrl+MMouse = Override Cache (new tab)
Alt+MMouse = Reload All Tabs
Shift+MMouse = Google Cache (new tab)
Other available actions include "Reload Non-Pinned Tabs", "Reload Pinned Tabs", "Reload Unsuccessful Tabs", and "Set/Clear Retry Interval". These actions can be swapped in via the configuration dialog or accessed via context menu.
"Problem loading page"? Disabled by default, R+ can also be configured to automatically retry when it encounters most page loading errors. Give it a shot, then begin wondering how you ever lived without it!
NOTE: This add-on is designed to replace several aging extensions, such as "Reload", "Online Reload", "ReloadEvery", "Reload Non-Pinned Tabs", "Show Image", and "Show Picture". It's recommended you remove these and anything similar before installing R+.