07-09-2013 03:59 PM - edited 07-09-2013 04:09 PM
You can't within the stock browser. This is a major problem with the stock browser and it's not going to get fixed by BlackBerry it seems so there are three solutions I have for you.
1) Delete the bookmark and readd it with the proper URL (will position the bookmark at the top of your bookmarks list within the browser)
2) Download and install SiteBook from BlackBerry World. It's a free bookmarking utility for the PlayBook. It's got a small learning curve to it and it's pretty good. You can add/edit/delete bookmarks and assign them to groups. It's not bad but not 100% perfect. The developer has been asked several times to update some of the bugs (non-text characters such as #@*) etc can not be added to category names for example) but doesn't seem to care or update their app and it's been several months of waiting...But the good news is that it works pretty well and will autolaunch the web browser to the Bookmark you want. You have to have Sitebook running first. http://appworld.blackberry.com/webstore/content/21
3) Create a folder on your homepage called Bookmarks and within in the stock browser, swipe down to reveal the URL bar and specifically the white star with a plus sign icon. Click that star with a plus icon and a dialogue box will appear, select Add to Home Screen. This will create a shortcut to your webpage (it's essentially a bookmark shortcut). Now press on the new shortcut and drag that icon into the Bookmarks Folder you just created and you can organize things how you see fit.
None of these are ideal. But in my opinion, I'd most definitely download and install Sitebook from BlackBerry World. It's the most useful I find. You can backup your bookmarks too and import them.