You cannot simply convert extensions / plugins / add-ins from one web browser to another, for example from Chrome (.crx) to Firefox (.xpi). However, the crx-to-xpi tool can be used to perform crx to xpi port.
You will have to find a proper plugin for your specific web browser, if the developer made version for another browser. The good thing is, good plugins are usually available for most web browsers, to cover whole market.