I don't use the Tabs plugin, so can't give you a definitive answer, but I do use FCKeditor in a tabs component I built myself, so I have encountered the problem before.
The problem is that when FCKeditor is created from a textarea which is not yet visible, it is given a height and width of 0. This appears to be true whether you define a width and height or not.
I have two solutions. The first (easiest) is to not load up the Tabs code until /after/ the FCKeditor instances have been displayed on screen. This is usually okay, as it should only take a millisecond or so for the browser to figure out all the proper widths and heights, then you can run the Tabs code.
The second is more complex. As I said, I wrote my own Tabs component, so I could adapt it to this. In my case, the FCKeditor code is only run on the shown tab, and whenever you go to a new tab, it is run again on just that tab. So, when a new tab is shown, temporarily (too quick for the mind to really notice), the original textarea is shown, before it is replaced by an FCKeditor instance.
RE: Editor resizes in comb. with Jquery Tabs
The problem is that when FCKeditor is created from a textarea which is not yet visible, it is given a height and width of 0. This appears to be true whether you define a width and height or not.
I have two solutions. The first (easiest) is to not load up the Tabs code until /after/ the FCKeditor instances have been displayed on screen. This is usually okay, as it should only take a millisecond or so for the browser to figure out all the proper widths and heights, then you can run the Tabs code.
The second is more complex. As I said, I wrote my own Tabs component, so I could adapt it to this. In my case, the FCKeditor code is only run on the shown tab, and whenever you go to a new tab, it is run again on just that tab. So, when a new tab is shown, temporarily (too quick for the mind to really notice), the original textarea is shown, before it is replaced by an FCKeditor instance.
This also works with CodePress.