One of the financial portal provides information about stocks I'm
interested in. Accessing this information requires filling a comlex
form, that sends data using HTTP POST method. I'm interested in
caching HTTP Request on the client-side (browser) and re-sending it
every week. Caching HTTP Response doesn't make sense in this
application context, because stock data changes quite often.

I know it is not recommended to cache HTTP POST request, because by
definition it not an idempotent operation (http://tinyurl.com/yj2mge6).
However, in this case it behaves as idempotent HTTP GET operation: it
provides read-only access to particular data. I know it is also
possible to send HTTP POST request without filling the form by
programmatically generating HTTP Request header (e.g. using jQuery,
JavaScript in general, or PHP) and then display the HTTP Response
(http://tinyurl.com/yjsjprp).

It would be also nice to bookmark HTTP POST request directly from a
browser. To automate the whole process the script on the client-side
should catch the HTTP POST Request on the fly and bookmark it upon a
user action. I believe it is possible though I still have no idea how.

However, before I start programming such a functionality/script I
wonder is there any off-the-shelf plugin/tool that realizes this
functionality. Do you know any?

Best regards,
Maciej