The decision to do this was already made in discussion over IRC; I am filing a bug so that the discussion and rationale has a more permanent impact. In bug 689742, hardware acceleration was disabled in Thunderbird because it was providing a distinctly worse user experience by using discrete GPUs. In the intervening two years, the graphics situation has changed, and the use of discrete GPUs apparently now requires use of WebGL, so the negative effects originally experienced should no longer be present (this is as discussed in bug 949756 comment 8). Instead, our disabling of hardware acceleration but not a myriad of other graphics preferences puts us in an untested situation of graphics code. The current week alone has seen two separate comm-central-only bustages due to the lack of this preference. In light of the changing situation, the decision was made to revert the changes in bug 689742 and restore Thunderbird to the same graphics configuration as Firefox.

JFTR, this change made Thunderbird scroll jerky again (in the mail list pane, most notably in an unmaximized TB window) on my Win7 64bit system with AMD Radeon HD 7700. Manually setting "gfx.direct2d.disabled" to "true" reverted TB to perfectly smooth scrolling in the mail list pane (and everywhere else).

(In reply to David.P from comment #2) > JFTR, this change made Thunderbird scroll jerky again (in the mail list > pane, most notably in an unmaximized TB window) on my Win7 64bit system with > AMD Radeon HD 7700. > > Manually setting "gfx.direct2d.disabled" to "true" reverted TB to perfectly > smooth scrolling in the mail list pane (and everywhere else). David, does this still reproduce for you when using version 38 with gfx.direct2d.disabled false?

(In reply to Wayne Mery (:wsmwk, use Needinfo for questions) from comment #3) > (In reply to David.P from comment #2) > > JFTR, this change made Thunderbird scroll jerky again (in the mail list > > pane, most notably in an unmaximized TB window) on my Win7 64bit system with > > AMD Radeon HD 7700. > > > > Manually setting "gfx.direct2d.disabled" to "true" reverted TB to perfectly > > smooth scrolling in the mail list pane (and everywhere else). > > David, does this still reproduce for you when using version 38 with > gfx.direct2d.disabled false? Nope, mail list scrolling actually seems to have improved with gfx.direct2d.disabled set to false.

(In reply to David.P from comment #4) > (In reply to Wayne Mery (:wsmwk, use Needinfo for questions) from comment #3) > > (In reply to David.P from comment #2) > > > JFTR, this change made Thunderbird scroll jerky again (in the mail list > > > pane, most notably in an unmaximized TB window) on my Win7 64bit system with > > > AMD Radeon HD 7700. > > > > > > Manually setting "gfx.direct2d.disabled" to "true" reverted TB to perfectly > > > smooth scrolling in the mail list pane (and everywhere else). > > > > David, does this still reproduce for you when using version 38 with > > gfx.direct2d.disabled false? > > Nope, mail list scrolling actually seems to have improved with > gfx.direct2d.disabled set to false. David, can you try the current beta with HWA enabled (and with gfx.direct2d.disabled true) and tell us if you still see the problem? http://www.mozilla.org/en-US/thunderbird/channel/