[Buildbot] #3662: build log text is not selectable in Firefox

[Buildbot trac]

#3662: build log text is not selectable in Firefox
----------------------+-----------------------
Reporter:  rutsky     |      Owner:
    Type:  undecided  |     Status:  new
Priority:  major      |  Milestone:  undecided
 Version:  0.9.3      |   Keywords:  www
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 To reproduce:

 1. Open some build, for example
 https://nine.buildbot.net/#/builders/2/builds/88522 in Firefox (I'm using
 50.1.0).

 2. Expand one of the steps, e.g. `git-buildbot`. Log of the step will
 appear.

 3. Try to select some log text with left mouse button - in Firefox text is
 not selected.

 Log text is selectable in Chromium. Also log text is selectable in Firefox
 if I open whole log (click on "view all xxx lines").

 Environment: Firefox 50.1.0 on Ubuntu 16.04.

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Ticket URL: <http://trac.buildbot.net/ticket/3662>
Buildbot <http://buildbot.net/>
Buildbot: build/test automation