Why doesn't Ctrl + F5 work in Firefox?
Moving the comment from Grzegorz into a Community-wiki answer.
This problem occurs because Xubuntu uses Ctrl+F5 to switch into fifth workspace (if you don't have as much workspaces, then simply nothing happens), in fact whole F1-F12 range is reserved.
There are two possible solutions:
- Redefine (clear) shorcut in Xubuntu (via Settings→Settings Manager→Window Manager→Keyboard) or
- Use alternative i.e. Ctrl+Shift+R.
You must press Ctrl+Shift+R to overwrite the cache in Xubuntu