Whilst this won’t resolve your current issue of the forum software eating a post. Try previewing the post before you actually post, that appears to reduce the instance of the post being eaten.

You can also try the back button in your browser, some will still have retained the post data and not just refreshed the page.

As you can see from my signature I use the latest firefox version (my default browser), winXP Pro SP3 and the latest avast free version 17.2.2288 and I have no problem using firefox.

I thought Lazarus was dead (excuse the pun) for firefox (last updated 10 August 2011), I had to give it up at one point as it was blocked by firefox checks. Unless you are using an old firefox ?

I have been using the Form History Control firefox add-on, try using firefox and log-on to your my.avast.com account. If it allows that then you should be able to go directly to the avast forum without having to log-on again.