The browser's BACK button:
If one presses the browser's BACK button after changing
one of the the browsing options, the browser will enter an undefined state
that can lead to making the site un-navigable (i.e. pressing the BACK button
must not cause a transition from one viewing option to another).
For example, consider displaying the "Contact" page
while in the "one frame" mode, then switching to the "two frames" mode,
and then opening the "About us" page. In this state, by pressing the BACK
button the site will be brought in an undefined state (because the threshold
between the two browsing modes has been crossed when pressing the BACK button).
The BACK button can be safely used for moving back
and forth between successively opened pages if none of the browsing option
has been changed while opening the respective pages.
Opening the pages
When opening a page (by clicking on it in the left
window pane), the pages should be left to download completely. If a page
transfer is interrupted, then any further attempt (in the current session)
to reopen it will bring on screen the uncompletely downloaded page.
If a page transfer has been interrupted, the workaround
is to "select" the frame in the right window pane (click inside the frame
without hitting a link) and selecting "reload frame" from the browser's
menu.
By closing and then restarting the browser one also
forces all the pages to be reloaded when accessed.