It is surprisingly poor written to me. This are some of the thing that has to be changed:

  1. input tag is self closing - options.html
  2. When using jQuery you should not use document.getElementById, innerHTML - notification.html
  3. function pausecomp(millis) seems like "busy waiting" - background.html
  4. html tags interpreted ( wow )

Edit:

 1. It is more of a must than can, actually [w3][1]. Inputs must be self closing unlike in the file options.html, where all of them are like:
    
    `<input>...</input>`
 2. When jQuery is used there is no reason to continue with the usage of:
    1. `document.getElementById` - jQuery provides selector - **$('#...')**
    2. `innerHTML` - jQuery provides method - **$().html()** 
 3.  agreed.
 4. If a question from Stackoverflow, for example like [this][2], contains html tag with **<>**, the tag is interpreted. So you will receive this question with an actual input. Maybe I should write something there, like sanitize - http://xkcd.com/327/.

Something new to fix:

 1. Using both `new Array` and `[]` is sign of bad style. You should chose one, and as *Crocford* and *SO community* **strongly** suggest it should be `[]`

Update: 

 - code style - a good practice is to use curly brackets, even if they are not needed now. This will produce a code which will be easier to update(options.html):


Use

    if (condition)
    {
    // code ...
    }else{
    // code ...
    }

instead of

    if (condition)
       // code ...
    else
       // code ...

 - Another optimization - for cycle, from [MDN][3](notification.html)




  [1]: http://www.w3.org/TR/html4/interact/forms.html#h-17.4
  [2]: https://stackoverflow.com/questions/5934300/c-inserting-input-in-htmldocument
  [3]: https://developer.mozilla.org/en/a_re-introduction_to_javascript#Arrays