The following add-ons are known to cause conflicts with Blank Canvas Gmail Signatures. Some people have reported that it is enough to just disable all add-ons, then re-enable them one by one starting with BC Gmail Signatures. This manual reset seems to fix some comflicts.

If you know of a conflict or one of the add-ons below no longer conflicts, let me know.

• Better Gmail 2 - This add-on seems to clash with Better GMail2 skins, specifically the dark skin. The address, subject, and compose windows go over-sized whenever you click on the compose signature button, and the save signature button, as well as other info at the bottom of the compose screen are hidden by the over-sized message body box. Enlarging and shrinking the window contents doesn't help. This happens with 100% consistency. The only fix found so far is to un-check the Skins option in Better Gmail2 add-on, compose the signature properly in this add-on, then recheck the  the dark skin.
  
  
• IE Tab - Some people have reported that disabling this add-on has fixed problems they were having with the Blank Canvas Gmail Signatures add-on, but it works just fine for me with no errors.
  
  
• Google Preview - Some people have reported that disabling this add-on has fixed problems they were having with the Blank Canvas Gmail Signatures add-on. It worked fine for me with no problems for a while (v3.12) and then suddenly started causing problems. I disabled it and BC Gmail Sigs works again. Try using BetterSearch instead
  
  
• Googlepedia - Shows you a relevant Wikipedia article along with your search results.
  
  
• Syncplaces - Synchronizes your bookmarks between different browsers. I recommend Foxmarks as a MUCH better alternative that doesn't cause any conflicts.
  
  
• Toolbar Buttons - A button pack for Firefox, Thunderbird and Sunbird