Is it possible to use F Secure Seach with other browsers e.g Mozilla?
Yes, this is possible.
But does you mean F-Secure Search (toolbar) or just F-Secure Search as Search page (like search.f-secure.com)?
if F-Secure Search for desktop installations (toolbar including) - so... you able to use it too.
If your browser is Internet Explorer (as default one browser / system browser for opening web-pages) and Search configured there. You have probably two workarounds to get it under Firefox:
--> Manual install extension for Firefox (from F-Secure Online Safety folder about Safe Search).
Like "extension"-file re-transfer to Firefox page about extensions. Should be trigger for installation extension.
And enable it.
--> Re-change default browser to Firefox. And restart system. It should to trigger F-Secure prompt for Safe Search installation automatically (with your setting).
You able to re-change default browser back to your previous (after this steps).
Troubles with this workarounds - potentially any updates for toolbar/extension should be upgraded manually.
Sorry if you ask about something else.
And sorry for my long reply.