You will need to install a user script manager extension to install this script.
(Don't worry, the script won't upload your information to anywhere!)
(Some texts are in Chinese in the following screenshots, but I think it does not matter too much :)
Hover your mouse over "settings" in the navigation bar and click the "Import osu!.db" button in the popup menu:
Select your osu!.db database file after clicking the button:
The script will begin to parse your osu!.db database, during which time the page will freeze and not respond to any user input. In Firefox the process may take up to around 5 seconds, and in Chrome the processing time will be much shorter. Please be patient and I'm going to fix this soon(or you can fix it before I do XD).
After the script finishes reading the database file, your owned beatmaps will be highlighted in the way osu!lazer does:
Beatmap download links in forum, wiki and beatmap pack listing page are also highlighted if you own corresponding beatmaps. In the case you don't own the beatmap, a download link is provided so that you don't need to go to the beatmap detail page to download it. One mouse click and several MB of Internet traffic saved!
As long as you don't close the tab or the window, you won't need to upload the database again. However, any newly downloaded beatmaps won't be recorded. This is also going to be fixed soon.
Here's my osu!mania profile page:
Here's a detailed listing of all the functionalities:
Hope you could be satisfied with the script! Have fun and leave your comment if you get any problem.