Firefox and Forum PHP

[#1]

There must be a solution posted somewhere but I'm sick and tired of this.....
I'm browsing the forum and click a link, it might be 'Unread Posts' or anything like that leading to a PHP page and Firefox pops up a box asking me what I want open the page with, Firefox being the default. If I agree the page is downloaded as a file and I get asked what I would like to use to open the file etc etc.
If I cancel the first box and re click the link there is a delay and the page eventually opens.
It doesn't always occur and is not a major problem....just annoying.

[#2]

No there isn't
I used to have the problem al the time but I could never find out the reason.
I installed Firebug to monitor the site so I could pick up what was causing the problem - you have guessed the answer - it hasn't happened since 

[#3]

Strat,  If I've had a problem with Firefox or Thunderbird I've always got an answer from mozillaZine Forums.  They're excellent at sorting out problems.
http://forums.mozillazine.org/index.php?sid=9b03c54a22f9b1f948fd5cc41a20f4af

[#4]

This would lend itself to being more of a server related problem than a client - the server should be parsing the file and running it - but the fact that it is attempting to forward it on as a download would indicate that for whatever reason, the server has failed to recognize that it is to run the file itself.