Well... *no* entries appear in the Error Console, in either Namoroka or Minefield, despite repeated attempts, though the effect is clearly visible.
Meanwhile, I've played with it a little more - the problem is *more general* than I assumed.
It happens at *multiple* browser widths for given tab width settings:
* for an even number of tabs
* for n tabs, every n pixel difference in browser width
* when browser width <= ( total width of tabs at "Maximum" width + default padding on tabbar )
Also, I stated it happened for 4 tabs at browser width 800px - I was wrong - more careful testing shows it to be exactly 801px ...
( Someone admitting to being wrong ? That doesn't happen often on the Internet
Using the TMP default tab widths: Minimum = 100px and Maximum = 250px
Here are some examples:
For 2 tabs - a sequence of 2 pixels:
browser widths: 510px 508px 506px 504px 502px 500px ... etc
For 4 tabs - a sequence of 4 pixels:
browser widths: 1009px 1005px 1001px 997px 993px 989px ... etc
For 6 tabs - a sequence of 6 pixels:
browser widths: 1508px 1502px 1496px 1490px 1484px 1478px ... etc
For 8 tabs - a sequence of 8 pixels:
browser widths: 1503px 1495px 1487px 1479px 1471px 1463px ... etc
It is possible to make the tabs jump back-and-forth between the correct and collapsed widths:
1: open an even number of tabs, with the browser window initially wider than the total width of those tabs
2: *slowly* narrow the browser window
Again, although the effect is clearly visible, no entries appear in the Error Console.
Attached are the TMP settings - though as stated, the settings are default except for using Mutli-row tabbar instead of scrolling tabbar...