This is pathetic.
You guys are in a thread that pops up #1 on Google for "opera refresh all tabs", yet you still aren't able to provide a solution.
Here I go:
Tools > Preferences (Ctrl+F12) > Advanced > Shortcuts > Under Keyboard shortcuts (bottom), click Edit "Opera Standard" > Expand "Application (defaults)" > Click New > Under "Input context and shortcuts", enter "Platform Windows-Unix-MCE, F5 ctrl" > Under "Actions", enter "Reload all pages" > Click OK > Click OK
Thanks for the tip, but F5 has always worked for me in Opera 9.5 and up. In Opera 9.2 and below the option was set to Ctrl + F5. So you could just switch to that layout and have the functionality back that way as well.
Topic will now be closed since there are solutions posted and this topic is just about 10 months old.
There was another topic in this forum about how to do this. Sadly it didnt have this exact title.