Wikipedia:BYPASS

In Apple Safari:

In Chrome and Firefox for Mac:

To speed things up and conserve communications bandwidth, browsers attempt to keep local copies of pages, images, and other content you've visited, so that it need not be downloaded again later. Occasionally this caching scheme goes awry (e.g. the browser insists on showing out-of-date content) making it necessary to bypass the cache, thus forcing your browser to re-download a web page's complete, up-to-date content. The rest of your cache is not affected.

In unusual circumstances, it may be worth clearing the entire cache (of your local browser).

Use one of the following:

On Windows, use one of the following:

On Mac OS X:

On Linux:

These instructions work for Firefox, SeaMonkey, and other related browsers.

On Windows and Linux, use one of the following:

On Mac OS X, use one of the following:

For version 4 and newer:

For version 3 and older:

Note that Apple claims that clicking the "Reload" toolbar button has the same effect as ⌘ Cmd+R, but this is not true; frequently the button will not bypass the cache.

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Wikipedia