Many folks were having an issue with this plugin not showing after a crash or fresh install. Try this solution I found because it certainly helped me - I had the same problem. This is for Windows.
1. add a new browser to your scene.
2. uncheck local file top left. click "browse".
3. got to the obs animated lower thirds folder, then click on lower thirds folder.
4 *Important* --- On the "browser-source.html" file, HOLD THE SHIFT KEY AND RIGHT CLICK - SELECT "COPY AS PATH". paste into the file area and REMOVE quotes "" from the beginning and end of the paste. Scroll down and check boxes for "Shutdown source and Refresh Browser" - click ok. This should work, it worked for me after much rresearch.
1. add a new browser to your scene.
2. uncheck local file top left. click "browse".
3. got to the obs animated lower thirds folder, then click on lower thirds folder.
4 *Important* --- On the "browser-source.html" file, HOLD THE SHIFT KEY AND RIGHT CLICK - SELECT "COPY AS PATH". paste into the file area and REMOVE quotes "" from the beginning and end of the paste. Scroll down and check boxes for "Shutdown source and Refresh Browser" - click ok. This should work, it worked for me after much rresearch.