Yes you can. Here is an example. In some mailers like HogmailerPlus, I am given a list of sites to choose for sending my email. One or two clicks, NP, but when given a list of 12 clickboxes is tedious.
I created a small javascript program that operates on the current webpage that sets all checkboxes. The "code" is fully contained in the URL field of a bookmark. And yes, I also have another bookmark that un-sets all checkboxes on the page.
The logic is simple. It loops through every html tag "checkbox" on the page, and sets the value of "checkbox" to true.
How to create this hack
Add a new bookmark. Name it "Checkbox On", then enter this code into the URL field:
javascript: (function() {
var aa= document.getElementsByTagName("input");
for (var i =0; i < aa.length; i++){
if (aa[i].type == 'checkbox')
aa[i].checked = true} })()
Save the bookmark.
To use this code
Navigate to the page where the clickboxes live, and just click the bookmark. All checkboxes will be checked.
Turn off all checkboxes
In a new bookmark named Checkbox Off. Simply use the same code, except aa[i].checked = false