User-Agent: Mozilla/5.0 (Windows; Windows NT 6.1; WOW64; rv:2.0b2pre) Gecko/20100720 Minefield/4.0b2pre Build Identifier: Mozilla/5.0 (Windows; Windows NT 6.1; WOW64; rv:2.0b2pre) Gecko/20100720 Minefield/4.0b2pre If you perform some action, you will find the words in the History Sidebar does not look the same. The STR below is the easier way to reproduce this bug. Reproducible: Always Steps to Reproduce: 1. Press the history button(I assume that you have this in your navigation toolbar) 2. You see the history sidebar 3. Close the history sidebar by pressing the history button again 4. Repeat this for a few time. 5. You can see the words in the history sidebar become bolder/less sharper Actual Results: Words become less sharper/bolder Expected Results: Words remain the same regardless of what user do.

Another way to reproduce this: 1. Go to ThunderBird 2. Go to your inbox 3. Open an web link from ThunderBird opening a new tab in Firefox. 4. Repeat this a few times(5-9 times) 5. Open the history sidebar 6. you will also see the error.