It is greyed out because it is still running. Once you get over the hurdle that filtering is not instantaneous I am thinking you will have less trouble.

Do you have filter logging enabled? How large is the filterlog.html file in your profile folder. (there will be one for each account in the sub folders (account folders) of mail in the profile folder.

Thanks. I'm used to filtering not being instantaneous (but thanks for the comment anyway). This seems to be a different type of problem. It happens for both very simple filters and some very long ones. "Run Now" stays greyed out for a very long time, or sometimes permanently. I'm having trouble reproducing the symptoms but suspect that it might be related to how I changed some filters to first copy a message to Local folders and then move the message to Trash. I did this to keep files I thought I was deleting from piling up in All Mail. I'm wondering if I accidentally set up a circular routine that Thunderbird can't exit from.

Regarding the greyed out Run Now button for filters, here is a better description of the issue: > If I run a filter and there are messages that are being filtered, the Run Now button will be greyed out. That is the behavior I'm used to while filtering is in progress and the blue activity manager bar is visible. > After filtering, however, the Run Now button remains greyed out and the activity manager indicates nothing is happening. Clicking on Run Now does nothing. > If I simply select/highlight a different filter, but don't run it, the button is black. > If I go back and select the first filter (not clicking on Run Now) the Run Now button is now black again and the filter can be run. > It appears that if there are no messages to filter when Run Now is clicked, the button remains black. It only turns grey and remains grey forever if at least one message is filtered and if I don't select/highlight another filter.

Thanks if you have time to suggest something. Sorry if I'm missing something obvious or have set up filters that cause the problem by a combination of Move, Copy, and Delete.