hello lse123, first a disclaimer: i'm in no way a web developer, so i don't know if the following advice will work under all circumstances or is the optimal way to proceed...

however when playing around with firefox' inbuilt web-developer tools (page inspector&style editor) it appears that when you add style="float: left;" at the end of the first table element in #mainContent in processorquote.php & booking-review.php the content is aligned as expected:

example:

< table width="100%" cellspacing="1" cellpadding="1" border="0" style="float: left;">

There appears to be a shift to the right if the minimum text size is increased and the menu line doesn't fit anymore on one line.
Such issues are usually caused by a missing style="clear:both" rule in combination with floating content.
Adding a clearing DIV at the end of that #header DIV that contains the menu bar or an extra clearing DIV between the #header DIV and the following #sidebar1 DIV should fix this.

style="clear:right"

Thks used this ^ to table in main content... with "both" rather "right" shifts below...

can remind me what clear do, or give url?

If there isn't a clear rule then Firefox starts to render content right after previous (floating) content ends if there is sufficient room and in cases where a menu or content wraps unexpectedly because a larger font is used then following content also may not fit anymore and also shifts to the right or down.
If you take a close look then you can usually spot this because that content doesn't start at the begin of line, but right after the end of the previous line.

See:

• https://developer.mozilla.org/en-US/docs/CSS/clear
• https://developer.mozilla.org/en-US/docs/CSS/CSS_Reference