A brief description of some fundamentals of Simple Highlighter. This is taken from an email I sent to someone, but it may help others.
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When you highlight some text on a page (and choose to highlight it), the 'unsaved highlights' icon appears (pen with a red star next to it). Clicking it shows the popup window, and the green icon thing with a + sign on it means the *location* of the highlight on the page is stored temporarily (remembered when you go back to the page, but forgotten when the browser or computer is restarted). The red icon thing with + sign on it stores the location persistently (remembered even when the browser or computer is restarted). When the current highlights are stored, the pen shows a red or green tick next to it.

The important thing to remember is that all that is stored is the address of the page (so when it's next loaded it's recognised), and at what point on the page to start & end the highlight. In other words, as long as when you next go to the exact same address the exact same page is sent to your computer (or at least in the important parts), it'll probably work. If there's something else in the location of the highlight the next time, then that'll be highlighted instead. So all that happens when you load a page you've highlighted *and then stored* (via one of those 2 buttons I said), is it 'replays' a series of commands specifying the position of the highlights (eg: start at line 7, highlight 10 characters in yellow).

As you can see it's hard to save the highlights with the page, because it's a 2 stage operation (load the page, THEN 'play' the highlights into it), but if you save the page in 'Webpage Complete' mode (not Webpage HTML only), they do show up (though they look a bit different). Some sites (especially Facebook) have tricks that make it hard or impossible to 'replay' the highlights because different content is shown for the same addresses, so it's best to learn which they are and save them beforehand.

Also, the 7th button along on the popup window (with an arrow pointing right) shows a summary of the contents of the highlights, and this can be saved as a separate file.

In the extension's options page you can see a list of the pages that you've stored highlights on, enable/disable highlights, assign keyboard shortcuts, automatically store highlights when you make them, or export the highlights database (which is the list of commands to highlight positions on the page, and the address of the page they're associated with).

For example, to assign the key 'm' to the first highlight (usually Red), in the 4 boxes next to 'Shortcut' on the 2nd page of the options page, the first 3 would be set to empty (unless you want to press another key at the same time), and the 4th has m in it. Note that certain websites can override shortcuts, and some just plain don't work or are used only by the browser.

Note that exporting/importing highlights isn't the same as the summary I explained earlier, but it is a way of 'sharing' the highlights with someone else, or making a backup. Ie: they 'import' your exported file into their database (on the options page), or they 'import' the file onto a specific page (via the icon with the yellow arrow on the popup window). But again
don't forget that is dependant on the page shown when you go to the address being the same each time. If for example the website has a redesign then the highlights can't be 'replayed' onto it, as it were, because everything is in a different place!