Copying content doesn’t always work on certain sites. For example, you can't copy an image from Photopea.com, which I rely on frequently. Saving the image to a file instead slows down my workflow too much. This is a known bug which has been around for a long time.
Password autofill was inconsistent. It didn’t work on some sites, like when accessing a Pi-hole dashboard. Maybe there’s an about:config tweak to fix this, but by that point I had already spent a lot of time troubleshooting other issues.
The bookmark menu closes after opening a single bookmark. If you like opening multiple bookmarks in a row, you have to keep reopening the menu and navigating to the next one each time, which is frustrating.
Twitch videos loaded slowly. I managed to fix this by deleting a specific file, re-creating it as a blank file, and setting it to read-only. This appears to be a known bug the developers are aware of.
Loading custom extensions is inconvenient. You can only load them temporarily unless you launch Firefox with a command-line option for each extension.
Create a list of what you want to be doing and consider attaching it to your monitor or putting it just to the side so that you can easily look at it. When you feel stuck, look at this list and do something on the list. Ensure the list includes some easy to do things on it like maybe "go for a walk", "read a book", "play instrument" etc.
When trying to change habits, start off small and simple. For example, if you want to start running each day you might start by putting on your running shoes and walking to the end of the driveway and back. Start off so small that your brain can't talk you out of it.
I create daily todo lists and feel satisfaction from checking them off.
Try some ideas and see what works for you. Good luck!