How can I always force a reload for some url?

Go to Firefox address bar and type:

about:config

type this into the filter:

browser.cache.check_doc_frequency

change the value to:

1

If Firefox value be number 3 only check if it seems outdated.

If Firefox value be number 2 always use cached version.

If Firefox value be number 1 always check for newer version.

If Firefox value be number 0 check for newer version once per session.

Look at this thread for a number of solutions.

Although none disable cache for a particular URL, there are options to turn off cache or use private browsing where nothing is cached. If you have a control over the page, then you can turn off caching this page using POST instead of GET, or using Cache-Control: no-cache in the webpage.