Firefox 5 ‘caching’ 301 redirects

In Firefox you have the “Web Developer” Tools (Ctrl+Shift+I). You can click “Network” tab and check the checkbox “Disable Cache” to check for new version of page every time. Then load the original URL and it will refresh your cache. Then you can enable the cache again and access that URL also from other tabs.
So you don’t need to clear your full cache.

From cptstubing06’s comment, the following can help clear the cache:

1. Type Ctrl+l to put the cursor on the location bar.
2. Type about:config to open the configuration settings.
3. Confirm any warnings.
4. Type browser.cache followed by Enter to filter the settings.
5. Double-click browser.cache.check_doc_frequency.
6. Change the value from 3 to 1.
7. Click OK.
8. Revisit the obsessively cached 301 page.
9. Reset the frequency back to 3 when finished.

Firefox should now redirect to the new 301 page, no longer fetching the redirected page from cache.