Lots of people use these type of add ons, but I wanted to mention it anyway in case you're not aware of them.
On a PC you tend to have a browser, and it can be distracting if you need to work.
LeechBlock allows you to block certain sites for a specific time period. It's a free add on and the most popular one of it's kind on Firefox.
Type in the URL of the site you want to block:
Enter a static time period when to block the site.
Or do what I do usually, and enter the amount of minutes per hour or day you can spend on the site.
You can add the timer in your bar too, it will count down and reset every hour / day, depending on your setting. If the timer reaches 0, you're blocked from the site until it unblocks you.
I use lots of Firefox addons, but I haven't a clue what I would use this one for. What does your browser have to do with working in Painter?
I suppose it would stop me from being tempted to stream grand tour cycling while working.
But then again, I could just not turn it on. :-P