Most Internet services don't prevent you from pasting information into password fields or other form fields on websites.
Some on the other hand restrict pasting to select fields or none at all, which means that you need to fill out those fields manually as you cannot use copy and paste to do so.
That's at least how it looks like on first glance. One example that I encountered just recently. I added a couple of items to a cart on this site and was asked to create an account to complete the purchase.
Both the repeat email address field and confirm password field are locked on the site blocking you from pasting text into them.
I use KeePass to generate unique passwords for websites and paste the information into the forms. Since I was not able to do so for one field, and had no desire to type a 30+ character password into the confirm password field, I had to find a way to bypass the restriction.
Bypass the restriction
I'm using Firefox as my main browser which is why I demonstrate how it is done using it. All other "mainstream" browsers, Chrome, Opera and Internet Explorer, support Developer Tools as well, and you can usually launch them by hitting F12 while the page is open that you want to modify.
- Make sure the page with the form is the active tab in the browser.
- Hit F12 to start the Developer Tools. They are displayed in a frame at the bottom of the browser window in Firefox.
- Select the inspector icon (the left icon next to Inspector in the toolbar), and click on the Confirm Password field (or any other field that blocks pasting).
- Locate oncopy="return false" and double-click on it.
- Change false to true, and et voila, you can paste into the second field as well.
- Alternatively, delete the whole property and hit return in the end.
Note: The effect remains until you reload the website, meaning it is not permanent but only temporary. This does not appear to work in Chrome right now, check out the alternatives below.
If you don't like digging in code to resolve the issue, or if a site uses a different method to prevent you from pasting into select fields, then you may be interested in alternatives to the manual solution posted above.
Browser extensions make things more comfortable. Firefox users and users who run forks of the browser may install Disable clipboard manipulations which enables pasting among other things.
Users who run a Chromium-based browser can download and install Don't fuck with paste instead.